Time interval production measurement and energy storage performance analytics in renewable DC energy systems

ABSTRACT

A system and method in which production measurement for renewable energy is obtained in a storage-independent manner. Energy storage is separated out from the renewable generation to provide individual performance analytics in DC-coupled and AC-coupled renewable energy systems with critical and auxiliary loads. A monitoring unit uses device communication and metering to enable revenue-grade production measurement for renewable source and energy storage periodically at specified time intervals. The production measurement for the renewable source is obtained in a form that would be comparable to renewable installations without storage. Additionally, multiple energy flows may be used by the monitoring unit to arrive at a storage efficiency value that can be attributed to the storage unit and how the storage unit is operated in the renewable energy system. The storage efficiency quantifies efficiency losses arising from the use of a storage unit to estimate the actual impact of storage on energy production.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the prioritybenefit under 35 U.S.C. § 120 of the U.S. patent application Ser. No.15/374,331 filed on Dec. 9, 2016, which claims the benefit of the U.S.Provisional Application No. 62/269,162 filed on Dec. 18, 2015, thedisclosures of all of these applications are incorporated herein byreference in their entireties. This application also claims the prioritybenefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No.62/418,676 filed on Nov. 7, 2016, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to renewable energy systemssuch as, for example, Photovoltaic (PV) solar systems, having on-siteenergy storage. More particularly, and not by way of limitation,particular embodiments of the present disclosure are directed tomeasurement of the produced renewable energy in a storage-independentmanner along with the quantification of the efficiency of the energystorage unit-based system.

BACKGROUND

Renewable energy, like wind energy and solar energy, is increasinglybeing explored to meet the ever-growing demand for energy in anenvironmentally-responsible manner. A photovoltaic (PV) system is anexample of a renewable energy system that converts the sun's radiationinto usable electricity. PV systems range from small, rooftop-mounted orbuilding-integrated systems with capacities from a few to several tensof kilowatts, to large, utility-scale power stations of hundreds ofmegawatts. Some PV systems may be connected to an electrical grid toenable transmission and distribution of their generated-electricity toother participants in the utility market. On the other hand, some PVsystems, such as, for example, residential or small-scale PV systems,may be off-grid or stand-alone systems.

FIG. 1 is a simplified block diagram of an exemplary renewable energysystem 10 with on-site energy storage. In the present disclosure, a PVsolar system is used as an example of a renewable energy system.Therefore, the discussion herein is primarily provided in the context ofa PV solar system. However, it is understood that the discussion remainsequally applicable to other renewable energy systems as well. When therenewable energy system 10 is a typical PV solar system or PV solarsite, it may include a renewable Direct Current (DC) energy source 12 inthe form of a solar/PV array. The PV system 10 also may comprise anumber of Balance of System (BOS) components, three of which—a chargecontroller 14, a storage (battery) unit 15, and an inverter 16—are shownin FIG. 1 by way of an example. The BOS components 14-16 may balance thepower-generating sub-system of the solar array 12 with the power-usingside (the electrical load). For ease of illustration, only theAlternating Current (AC) electrical service interconnect point is shownusing block 18 in FIG. 1; any DC load portion is omitted. An AC load(such as, for example, a residential electrical load) or AC power grid(not shown) may receive the AC inverter output through the ACinterconnect point 18.

The charge controller 14 may regulate the electrical input received fromthe PV array 12 so as to satisfy the demand for the Direct Current (DC)load (not shown) and transfer any additional electricity for storageinto the battery unit 15. On the other hand, when the generatedelectricity (by the DC energy source or PV array 12) is not sufficientto satisfy the requirements of the DC load, the charge controller mayaccess the stored electricity from the battery unit 15 and supply it tothe DC load. The battery or storage unit 15 also may supply electricalenergy to an inverter 16, which may convert the stored electric currentfrom DC to AC to be delivered to the AC service interconnect point 18.The DC load (not shown) may represent systems or devices that operate onDC current, whereas the AC interconnect point 18 may serve systems ordevices that operate on AC current. Although not shown in FIG. 1, the PVsite 10 also may include additional BOS components such as, for example,power-conditioning equipment, structures and racking systems formounting various BOS components and solar arrays, electrical wiring,cabling, and interconnections, and other electrical accessories to setup a working PV site. In some implementations, the PV site 10 also mayuse a solar tracking system (not shown) to improve the system's overallperformance.

SUMMARY

As prices for storage decline, electric energy storage units—like thebattery unit 15 in FIG. 1—are increasingly collocated with renewableenergy systems. However, for billing as well as performance analytics,measurement of renewable energy production in general (and PV solar inparticular)—such as, for example, the energy production by the renewableenergy source 12 in FIG. 1—may need to be achieved independent of thecharging and discharging of energy storage at the same site so as toprovide an accurate measurement of the actual, usable quantity of thegenerated DC energy delivered as AC energy to the AC load.

Currently, AC output from the inverter such as, for example, theinverter 16 in FIG. 1, or DC input to the charge controller such as, forexample, the charge controller 14 in FIG. 1, is metered as representingthe produced energy. However, simply metering inverter output to the ACload as an indicator of renewable generation no longer works in case ofa storage-based renewable energy system, such as a PV solar system,because the observed inverter output is the result of solar generation(for example, by a PV array) with battery discharge power added to it orthe battery charge power subtracted from it, with the inverterefficiency superimposed on it. Furthermore, the inverter output also maybe affected by the storage/battery unit's efficiency of charging anddischarging the battery over the long term. Similarly, simply using thesolar current (output by a PV array) as measured by a DC sub-meter orreported by a charge controller directly as production measurement isinaccurate as well because it would measure the DC side of the renewablegeneration, but would not measure the actual usable quantity of thisenergy delivered as AC metered power. For example, the usable quantitymay be less than the produced energy when the battery is charging andmay depend on the inverter efficiency as well. Furthermore, DC-sidebased measurements do not accurately provide the correct timestamp whenthe power was actually delivered (to the AC load), which is oftenimportant for billing and system maintenance/analytics. Finally, suchmeasurements also do not accurately assign efficiency losses to therenewable source as a result of the energy storage round trip—that is,energy flow from the storage unit to the inverter and reverse flow fromthe inverter into the storage unit. This can be complicated by multiplefactors such as, for example, (a) how often the battery is charged anddischarged, (b) what depth of discharge is used to deliver to the ACload, (c) how the size of the renewable system (for example, the powergeneration capacity of solar panels) compare to the size of the storagesystem (for example, battery capacity/rating), and so on.

It is therefore desirable to obtain the production measurement forrenewable energy in a storage-independent manner—in a form that would becomparable to renewable installations without storage. This is importantfor accurate billing, maintenance, and performance analytics. It is alsodesirable to be able to quantify efficiency losses arising from the useof a storage unit to estimate the actual impact of storage and,possibly, the charge controller algorithm on energy production.

As a solution, particular embodiments of the present disclosure providefor methods to separate out energy storage from the renewable generationand also provide for performance analytics metrics on both—energystorage and energy generation—separately. Furthermore, certainembodiments of the present disclosure also describe methods to separateout energy storage efficiency as a metric and to calculate it indifferent types of systems with different data availability constraints.A monitoring unit as per teachings of the present disclosure uses devicecommunication and metering to enable revenue-grade productionmeasurement for renewable source and energy storage periodically atspecified time intervals such as, for example, every 5 minutes or every15 minutes. In the discussion here, the term “renewable source” may beused interchangeably with the term “renewable” to refer to differenttypes of renewable energy. The production measurement for a renewablesource is obtained in a form that would be comparable to renewableinstallations without storage, which is important for accurate billing,maintenance, and performance analytics. Additionally, in particularembodiments, multiple energy flows may be used by the monitoring unit toarrive at an efficiency ratio that can be attributed to the storage unitin the renewable energy system. This efficiency ratio can be used tode-rate expected AC energy from the renewable generation system tocompare with AC energy obtained in other systems—with or withoutstorage, or to separate the efficiency of the energy source (forexample, solar panel array) from the battery efficiency in combinedsolar-battery systems.

In one embodiment, the present disclosure is directed to a method formeasuring production of renewable energy in a storage-independent mannerin a renewable energy system. The method comprises: (i) determining eachof the following values during a pre-determined time interval: (a) an“S” value, wherein the S value is an interval-specific magnitude of afirst Direct Current (DC) energy flow from a renewable energy source toan intermediate unit in the system, (b) an “M” value, wherein the Mvalue is an interval-specific magnitude of a first Alternating Current(AC) energy flow between the intermediate unit and an AC interconnectpoint in the system, (c) a “C” value, wherein the C value is aninterval-specific magnitude of a second AC energy flow from theintermediate unit to a critical loads panel in the system, (d) an “A”value, wherein the A value is an interval-specific magnitude of a thirdAC energy flow from the intermediate unit to an auxiliary loads panel inthe system, and (e) a “B” value, wherein the B value is aninterval-specific magnitude of a second DC energy flow between theintermediate unit and a DC storage unit in the system; (ii) furtherdetermining an interval-specific net AC energy flow out of theintermediate unit based on a directional summation of the M, C, and Avalues; and (iii) using the S, M, C, A, and B values to calculate aportion of the interval-specific net AC energy flow attributable only tothe interval-specific first DC energy flow, thereby excludingcontribution to the net AC energy flow from the DC storage unit. Thismethod of production measurement may be used, for example, forDC-coupled systems with critical and auxiliary loads.

In some embodiments, the intermediate unit may include an inverter and acharge controller.

In one embodiment, the method includes generation of pricing for theinterval-specific first DC energy flow (from the renewable energysource) based on the calculated portion of the interval-specific net ACenergy flow.

In certain embodiments, the renewable energy is solar energy, and therenewable energy system is a PV solar system.

The discussion below provides a detailed description of productionmeasurement for a renewable source in a storage-independent manner indifferent types of renewable energy systems—DC-coupled as well asAC-coupled.

In one embodiment, the present disclosure is directed to a method formeasuring an efficiency of a DC storage unit in a renewable energysystem. The method comprises: (i) determining a sum of “S” values,wherein each S value in the sum is associated with a corresponding oneof a plurality of pre-determined time intervals and is aninterval-specific magnitude of a DC energy flow from a renewable energysource to an inverter in the system, and wherein the DC storage unit isoperatively connected to the inverter and configured to store DC energy;(ii) further determining a sum of (M+C+A) values, wherein each (M+C+A)value in the sum of (M+C+A) values is associated with a correspondingone of the plurality of pre-determined time intervals and includes: (a)an “M” value that is an interval-specific magnitude of a first AC energyflow between the inverter and an AC interconnect point in the system,(b) a “C” value that is an interval-specific magnitude of a second ACenergy flow from the inverter to a critical loads panel in the system,and (c) an “A” value that is an interval-specific magnitude of a thirdAC energy flow from the inverter to an auxiliary loads panel in thesystem; and (iii) calculating the efficiency of the DC storage unitusing the sum of S values, the sum of (M+C+A) values, and an efficiencyfactor for the inverter. This method for measuring storage efficiencymay be used, for example, for DC-coupled systems with critical andauxiliary loads.

In another embodiment, the present disclosure is directed to a methodfor determining an efficiency of a DC storage unit in a renewable energysystem. The method comprises: (i) determining each of the followingvalues during a pre-determined time interval: (a) an “M” value that isan interval-specific magnitude of a first AC energy flow between aninverter and an AC interconnect point in the system, wherein the DCstorage unit is operatively connected to the inverter and configured tostore DC energy, (b) a “C” value that is an interval-specific magnitudeof a second AC energy flow between the inverter and a critical loadspanel in the system, and (c) an “A” value that is an interval-specificmagnitude of a third AC energy flow from the inverter to an auxiliaryloads panel in the system; (ii) determining a sum of (M+C+A)_(out)values, wherein each (M+C+A)_(out) value is associated with acorresponding one of a plurality of pre-determined time intervals and isan interval-specific magnitude of net AC energy flow out of theinverter; (iii) determining a sum of (M+C+A)_(in) values, wherein each(M+C+A)_(in) value is associated with a corresponding one of theplurality of pre-determined time intervals and is an interval-specificmagnitude of net AC energy flow into the inverter; and (iv) calculatingthe efficiency of the DC storage unit using the sum of (M+C+A)_(out)values, the sum of (M+C+A)_(in) values, a DC-to-AC conversion efficiencyfactor for the inverter, and an AC-to-DC conversion efficiency factorfor the inverter. This method for determining storage efficiency may beused, for example, for AC-coupled systems with critical and auxiliaryloads.

In one embodiment, the present disclosure is directed to a monitoringunit for measuring production of renewable energy in astorage-independent manner in a renewable energy system. The monitoringunit is operable to perform the following: (i) determine each of thefollowing values during a pre-determined time interval: (a) an “S”value, wherein the S value is an interval-specific magnitude of a firstDC energy flow from a renewable energy source to an intermediate unit inthe system, (b) an “M” value, wherein the M value is aninterval-specific magnitude of a first AC energy flow between theintermediate unit and an AC interconnect point in the system, (c) a “C”value, wherein the C value is an interval-specific magnitude of a secondAC energy flow from the intermediate unit to a critical loads panel inthe system, (d) an “A” value, wherein the A value is aninterval-specific magnitude of a third AC energy flow from theintermediate unit to an auxiliary loads panel in the system, and (e) a“B” value, wherein the B value is an interval-specific magnitude of asecond DC energy flow between the intermediate unit and a DC storageunit in the system; (ii) further determine an interval-specific net ACenergy flow out of the intermediate unit based on a directionalsummation of the M, C, and A values; and (iii) use the S, M, C, A, and Bvalues to calculate a portion of the interval-specific net AC energyflow attributable only to the interval-specific first DC energy flow,thereby excluding contribution to the net AC energy flow from the DCstorage unit.

In particular embodiments, the monitoring unit may be operable toperform various tasks, operations, and method steps described above, butnot repeated here for the sake of brevity.

In one embodiment, the present disclosure is directed to a data storagemedium operable with a monitoring unit in a renewable energy system. Thedata storage medium may contain program instructions, which, whenexecuted by the monitoring unit, cause the monitoring unit to performthe following: (i) determine each of the following values during apre-determined time interval: (a) an “S” value, wherein the S value isan interval-specific magnitude of a first DC energy flow from arenewable energy source to an intermediate unit in the system, (b) an“M” value, wherein the M value is an interval-specific magnitude of afirst AC energy flow between the intermediate unit and an ACinterconnect point in the system, (c) a “C” value, wherein the C valueis an interval-specific magnitude of a second AC energy flow from theintermediate unit to a critical loads panel in the system, (d) an “A”value, wherein the A value is an interval-specific magnitude of a thirdAC energy flow from the intermediate unit to an auxiliary loads panel inthe system, and (e) a “B” value, wherein the B value is aninterval-specific magnitude of a second DC energy flow between theintermediate unit and a DC storage unit in the system; (ii) furtherdetermine an interval-specific net AC energy flow out of theintermediate unit based on a directional summation of the M, C, and Avalues; and (iii) use the S, M, C, A, and B values to calculate aportion of the interval-specific net AC energy flow attributable only tothe interval-specific first DC energy flow, thereby measuring productionof renewable energy by the renewable energy source in astorage-independent manner.

In certain embodiments, the program instructions, upon execution by themonitoring unit, may cause the monitoring unit to perform various othertasks, operations, and method steps described above, but not repeatedhere for the sake of brevity.

Thus, as per teachings of the present disclosure, the timeinterval-based production measurement for a renewable source is obtainedin a form that would be comparable to renewable installations withoutstorage. By making the measurement metrics directly comparable, systemowners can measure and manage their renewable assets in ways currentlyused by the market for optimization, financing, and securitization.These activities are critical to the continued growth of the renewableenergy market, and while energy storage is a key new capability, it maybe difficult without the methodologies of the present disclosure to usethe established processes to develop the projects, find off-takers forthe energy product, and efficiently manage the renewable assets.Furthermore, the present disclosure also provides a methodology toestimate the actual impact of storage and the charge controlleralgorithm on AC energy production. This estimation may be more usefulfor assessing system performance than the roundtrip energy storageefficiency metric alone. As is understood, the roundtrip storageefficiency number expresses the efficiency of putting a unit of energyinto storage and getting it back. However, not all energy may passthrough the storage in some renewable source systems. In other systems,all renewable energy plus additional energy from the AC grid may passthrough the storage. The overall storage efficiency metric expressed inthe present disclosure addresses this additional complexity and gives asingle number that can be used to explain the impact of the presence ofstorage and the charge control strategy on renewable energy production.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following section, the present disclosure will be described withreference to exemplary embodiments illustrated in the figures, in which:

FIG. 1 is a simplified block diagram of an exemplary renewable energysystem with on-site energy storage;

FIG. 2 lists different types of renewable energy systems addressed inthe present disclosure;

FIG. 3 is a simplified block diagram of an exemplary renewable energysystem according to one embodiment of the present disclosure showingvarious energy flows to be measured on a per-interval basis as perteachings of the present disclosure for calculations of renewable sourceproduction and system storage efficiency;

FIG. 4A shows an exemplary flowchart illustrating how renewable sourceproduction measurement may be performed in a storage-independent manneraccording to one embodiment of the present disclosure;

FIG. 4B depicts an exemplary flowchart illustrating how overallefficiency of a DC storage unit may be measured in a renewable energysystem according to one embodiment of the present disclosure;

FIG. 5 is a simplified block diagram of a DC coupled renewable energysystem (with critical and auxiliary loads) according to one embodimentof the present disclosure showing various energy flows to be measured ona per-interval basis as per teachings of the present disclosure forcalculations of renewable source production and system storageefficiency;

FIG. 6A shows an exemplary flowchart illustrating how renewable sourceproduction measurement may be performed in the system of FIG. 5 in astorage-independent manner according to one embodiment of the presentdisclosure;

FIG. 6B depicts an exemplary flowchart illustrating how efficiency ofthe DC storage unit in the renewable energy system of FIG. 5 may bemeasured according to one embodiment of the present disclosure;

FIG. 7 is a simplified block diagram of an AC coupled renewable energysystem (with critical and auxiliary loads) according to one embodimentof the present disclosure showing various energy flows to be measured ona per-interval basis as per teachings of the present disclosure forcalculations of renewable source production and system storageefficiency;

FIG. 8 depicts an exemplary flowchart illustrating how storageefficiency may be measured in the AC-coupled system of FIG. 7 accordingto one embodiment of the present disclosure; and

FIG. 9 depicts an exemplary block diagram of a monitoring unit accordingto one embodiment of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the disclosure.However, it will be understood by those skilled in the art that thepresent disclosure may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentdisclosure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present disclosure. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” or“according to one embodiment” (or other phrases having similar import)in various places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments. Also, depending on the context of discussionherein, a singular term may include its plural forms and a plural termmay include its singular form. Similarly, a hyphenated term (e.g.,“pre-determined,” “interval-specific”, “on-site,” etc.) may beoccasionally interchangeably used with its non-hyphenated version (e.g.,“predetermined,” “interval specific”, “on site,” etc.), and acapitalized entry (e.g., “Charge Controller,” “Battery Unit,” etc.) maybe interchangeably used with its non-capitalized version (e.g., “chargecontroller,” “battery unit,” etc.). Such occasional interchangeable usesshall not be considered inconsistent with each other.

It is noted at the outset that the terms “coupled,” “operativelycoupled,” “connected”, “connecting,” “electrically connected,” etc., areused interchangeably herein to generally refer to the condition of beingelectrically/electronically connected in an operative manner. Similarly,a first entity is considered to be in “communication” with a secondentity (or entities) when the first entity electrically sends and/orreceives (whether through wireline or wireless means) informationsignals (whether containing address, data, or control information)to/from the second entity regardless of the type (analog or digital) ofthose signals. It is further noted that various figures shown anddiscussed herein are for illustrative purpose only, and are not drawn toscale.

The terms “first,” “second,” etc., as used herein, are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.) unless explicitly defined assuch. Furthermore, the same reference numerals may be used across two ormore figures to refer to parts, components, blocks, circuits, units,signals, or modules having the same or similar functionality. However,such usage is for simplicity of illustration and ease of discussiononly; it does not imply that the construction or architectural detailsof such components or units are the same across all embodiments or suchcommonly-referenced parts/modules are the only way to implement theteachings of particular embodiments of the present disclosure.

FIG. 2 lists different types of renewable energy systems addressed inthe present disclosure. Broadly, there may be two distinct types ofrenewable energy systems: a DC-coupled system, and an AC-coupled system.In a DC-coupled system, the renewable energy (which is generated in theDC form) is supplied in the DC form to an inverter unit connected to abattery unit in the system. On the other hand, in an AC-coupled system,the generated DC renewable energy is first converted into an AC formbefore supplying it (in the AC form) to the battery-connected inverter.As noted in FIG. 2, FIG. 3 in the present disclosure shows an exemplaryDC-coupled system without critical and auxiliary (Aux) loads, FIG. 5shows an exemplary DC-coupled system with critical and Aux loads, andFIG. 7 shows an exemplary AC-coupled system with critical and Aux loads.The renewable energy production measurement and storage systemperformance analytics for each of these three systems are discussed indetail below.

I. DC-Coupled System Without Critical and Auxiliary Loads

FIG. 3 is a simplified block diagram of an exemplary renewable energysystem 20 according to one embodiment of the present disclosure showingvarious energy flows to be measured on a per-interval basis as perteachings of the present disclosure for calculations of renewable sourceproduction and system storage efficiency. As mentioned in FIG. 2, thesystem 20 in FIG. 3 is a DC-coupled system without critical andauxiliary loads. The renewable energy system 20 may be a PV solar systemand, hence, the discussion below may occasionally refer to solar energyand PV solar system instead of the corresponding general terms“renewable energy” and “renewable energy system.” As shown, the system20 may include a renewable DC energy source 22, an inverter unit 24, astorage (battery) unit 26, an AC service interconnect point (or AC mainservice panel) 28, and a monitoring unit 30. An AC load (such as, forexample, a residential electrical load if the system 20 is a residentialsystem) or AC power grid (for example, if the system 20 is a commercialsystem) may receive the AC energy through the AC interconnect point 28.In one embodiment, the renewable energy source 22 may be an array of PVsolar panels.

For simplicity and ease of analysis as per teachings of the presentdisclosure, an inverter, like the inverter 16 in FIG. 1 or a similarunit(s) having the inverter functionality of converting DC to AC, and acharge controller, like the charge controller 14 in FIG. 1, areconsidered as a combined entity in the form of the inverter unit 24 inFIG. 3. In the discussion below, any energy flow between these twoindividual entities will be ignored. Furthermore, although the inverterunit 24 may be occasionally referred to simply as an “inverter” in thediscussion below because of the relevance of its inverter functionality,it is understood that the inverter unit 24 includes charge controllerfunctionality as well. However, unless the context requires otherwise(for example, when the DC energy flow from the source 22 is discussed,the charge controller functionality may be more relevant), the mentionof the inverter unit 24 in the discussion below is primarily withreference to its inverter functionality. For example, the laterdiscussion of energy flow between the inverter unit 24 and the ACinterconnect point 28 refers to the energy flow between the inverter(not shown) within the inverter unit 24 and the AC interconnect point28. Similarly, the discussion of inverter efficiency should be construedto refer to the efficiency of the inverter portion within the inverterunit 24, and not to include the efficiency of the charge controllerportion. Although, for the sake of brevity, the inverter within theinverter unit 24 may not be mentioned every time inverter functionalityis discussed with reference to the inverter unit 24, such reference maybe implied from the context of discussion. Similarly, even if thegeneral term “inverter unit” is mentioned without more, thefunctionality under discussion may apply to its charge controllerportion only, as can be evident from the context of discussion.

It is noted here that the DC energy source 22 may be functionallysubstantially similar to the DC energy source 12 in FIG. 1, the inverterunit 24 may collectively provide substantially similar functionalitiesas are individually provided by the units 14, 16 in FIG. 1, the batteryunit 26 may be functionally substantially similar to the battery unit 15in FIG. 1, and the AC interconnect point 28 may be functionallysubstantially similar to the AC interconnect point 18 in FIG. 1.Therefore, the earlier discussion of various constituent units in FIG. 1applies to similar units in FIG. 3 and is not repeated here for the sakeof brevity. It is noted, however, that the system units 22, 24, 26, and28 in the renewable energy system 20 in the embodiment of FIG. 3 aredifferent from similar units in FIG. 1 in the sense that the units inFIG. 3 are configured to be operatively connected with the monitoringunit 30 as shown by respective dotted arrows 32-35. One or more of theseconnections may be wired or wireless. In some embodiments, themonitoring unit 30 may be located off-site and may be in communicationwith the system units 22, 24, 26, and 28 via a communication network(not shown) such as, for example, an Internet Protocol (IP) basednetwork like the Internet. As discussed below, in certain embodiments,energy flow metering may be integral to one or more of the system units22, 24, 26, and 28, in which case the system unit(s) may periodicallyreport relevant energy flow measurements to the monitoring unit 30 viaits respective connection—direct or indirect (such as through anetwork).

Exemplary architectural details of a monitoring unit, such as the unit30 in FIG. 3, are shown in FIG. 9, which is discussed later below. It isnoted here that the monitoring unit 30 may be configured (in hardware,via software, or both) to implement some or all of the renewable sourceproduction measurement and storage efficiency determination aspects asper teachings of the present disclosure. For example, when existinghardware of the monitoring unit 30 cannot be modified, the productionmeasurement and efficiency determination methodologies according toparticular embodiments of the present disclosure may be implementedthrough suitable programming of one or more processors in the monitoringunit 30. Such processor(s) may be, for example, the processor 116 inFIG. 9. Upon execution of the program code by a processor in themonitoring unit 30, the monitoring unit 30 may be operative to performvarious calculations discussed with reference to FIGS. 3-8. Thus, in thediscussion herein, although the monitoring unit 30 may be referred to as“performing,” “accomplishing,” or “carrying out” a function or process,it is evident to one skilled in the art that such performance may betechnically accomplished in hardware and/or software as desired.

As noted before, the monitoring unit 30 may be operatively coupled tothe units 22, 24, 26, and 28 in the system 20 via a communicationnetwork (not shown) and may receive and store equipment-specificinformation therein for the units 22, 24, 26, and 28. In one embodiment,the monitoring unit 30 may wirelessly communicate with one or more ofthese units via the network. Such wireless communication may be carriedout using a short-range wireless connectivity protocol such as, forexample, the Bluetooth® standard, a Wireless Local Area Network (WLAN)based connection, a Near-Field Communication (NFC) protocol, a protocolthat supports Machine-to-Machine (M2M) communication, and the like. Insome embodiments, the system 20 may include more or less or differenttypes of functional entities than those shown in FIG. 3.

In one embodiment, the network connecting the monitoring unit 30 withother units in the system 20 may be a packet-switched network such as,for example, an IP network like the Internet, a circuit-switchednetwork, such as the Public Switched Telephone Network (PSTN), or acombination of packet-switched and circuit-switched networks. In anotherembodiment, the network may be an IP Multimedia Subsystem (IMS) basednetwork, a satellite-based communication link, a WorldwideInteroperability for Microwave Access (WiMAX) system based on Instituteof Electrical and Electronics Engineers (IEEE) standard IEEE 802.16e, anIP-based cellular network such as, for example, a Third GenerationPartnership Project (3GPP) or 3GPP2 cellular network like a Long TermEvolution (LTE) network, a combination of cellular and non-cellularnetworks, a proprietary corporate network, a Public Land Mobile Network(PLMN), and the like.

In one embodiment, the monitoring unit 30 be a back-end systemcontaining a PV solar analytics database. The database in the monitoringunit 30 may be a proprietary data source owned, operated, or maintainedby, for example, a PV solar site installation/maintenance company. Incertain embodiments, the monitoring unit 30 may be an on-site monitoringunit that is in communication with various other on-site equipment—likethe units 22, 24, and 26—and may receive and store equipment-specificinformation in a memory unit (like the memory 119 in FIG. 9) in themonitoring unit 30.

In particular embodiments, the physical structure of the monitoring unit30 may include metering and/or communication ability to obtaininformation on all requisite kWh (kilo watt hour) energy flows in thesystem 20. In other words, as discussed in more detail below, themonitoring unit 30 may be able to receive energy flow-metering relatedinformation either from a dedicated, flow-specific meter or throughcommunication with the relevant unit 22, 24, 26, 28 having an integralcapability to meter and report the respective energy flow itself. Morespecifically, in particular embodiments, the present disclosure mayinclude the measurement and reporting of one or more of the followingenergy flows:

1. Renewable energy flow into the inverter unit 24 (in one embodiment,the charge controller portion of the unit 24), the kWh flow informationabout which may be obtained by the monitoring unit 30 in one of thefollowing ways:

(a) Through DC sub-metering on the DC renewable source(s). A dedicatedDC sub-metering equipment (not shown) may be installed to measure the DCenergy flow between the energy source 22 and the inverter unit 24. Theinstalled equipment may be operatively connected—through wired orwireless means—to the monitoring unit 30 and configured to report themeasured flow to the monitoring unit 30 automatically as required perteachings of the present disclosure or in response to each request fromthe monitoring unit 30.

(b) Through communication with the integrated DC inverter/chargecontroller unit 24, which may be configured to meter the incoming energyflow and provide the information on energy flow from the renewablesource into the inverter portion and the charge controller portionseparately, or the total integrated flow received from the energy source22. In one embodiment, the inverter unit 24 may provide the requisiteflow information automatically as required per teachings of the presentdisclosure, or in response to each request from the monitoring unit 30.

2. Flow to/from the inverter unit 24 from/to the battery unit 26. Thisflow may be reported as a net accumulated flow or disaggregated(directional) flow numbers in each direction—input to the battery unit26 and output from the battery unit 26. The kWh flow information aboutthis flow may be obtained by the monitoring unit 30 in one of thefollowing ways:

(a) As reported by the battery unit 26. The battery unit 26 may beconfigured to report the incoming and outgoing flow numbers for theenergy flow to/from the inverter unit 24 to the monitoring unit 30automatically as required per teachings of the present disclosure or inresponse to each request from the monitoring unit 30.

(b) As reported by the charge controller (when it is not integrated withan inverter). The charge controller may be configured to report theincoming and outgoing flow numbers for the energy flow to/from thebattery unit 26 to the monitoring unit 30 automatically as required perteachings of the present disclosure or in response to each request fromthe monitoring unit 30.

(c) As reported by the integrated inverter/CC unit 24. The integratedinverter/CC unit 24 may be configured to report the incoming andoutgoing flow numbers for the energy flow to/from the battery 26 to themonitoring unit 30 automatically as required per teachings of thepresent disclosure or in response to each request from the monitoringunit 30.

(d) Through DC sub-metering at the battery unit 26. A dedicated DCsub-metering equipment (not shown) may be installed at the battery unit26 to measure the DC energy flow between the battery unit 26 and theinverter unit 24. The installed equipment may be operativelyconnected—through wired or wireless means—to the monitoring unit 30 andconfigured to report the measured flow to the monitoring unit 30automatically as required per teachings of the present disclosure or inresponse to each request from the monitoring unit 30.

3. Flow to/from the inverter (when it is not integrated with a chargecontroller) from/to the AC main service panel/interconnect point 28.This flow may be reported as a net accumulated flow or disaggregated(directional) flow numbers in each direction—input to the inverter andoutput from the inverter. The kWh flow information about this flow maybe obtained by the monitoring unit 30 in one of the following ways:

(a) Through an AC watt-hour meter (not shown) installed at the AC mainspanel 28 to measure the energy flow between the inverter and the ACmains panel 28. The AC watt-hour meter may be operativelyconnected—through wired or wireless means—to the monitoring unit 30 andconfigured to report the measured flow to the monitoring unit 30automatically as required per teachings of the present disclosure or inresponse to each request from the monitoring unit 30. Alternatively, inone embodiment, the AC mains panel 28 (with in-built watt-hour meter)may be configured to communicate the relevant energy flow information tothe monitoring unit 30.

(b) As reported by the inverter. The inverter may be configured toreport the incoming and outgoing flow numbers—for the energy flowto/from the AC mains panel 28—to the monitoring unit 30 automatically asrequired per teachings of the present disclosure or in response to eachrequest from the monitoring unit 30.

4. Net kWh outflow from the battery 26 and net kWh inflow into thebattery 26. The kWh information about these flows may be obtained by themonitoring unit 30 in one of the following ways:

(a) Through DC sub-metering at the battery unit 26. A dedicated DCsub-metering equipment (not shown) may be installed at the battery unit26 to measure the DC energy flow to/from the battery unit 26. Theinstalled equipment may be operatively connected—through wired orwireless means—to the monitoring unit 30 and configured to report themeasured flow to the monitoring unit 30 automatically as required perteachings of the present disclosure or in response to each request fromthe monitoring unit 30.

(b) As reported by the battery unit 26. The battery unit 26 may beconfigured to report the incoming and outgoing flow numbers for theenergy flow to/from the battery unit 26 to the monitoring unit 30automatically as required per teachings of the present disclosure or inresponse to each request from the monitoring unit 30.

(c) As reported by the charge controller, if it is not integrated withthe inverter. The charge controller may be configured to report theincoming and outgoing flow numbers for the energy flow to/from thebattery 26 to the monitoring unit 30 automatically as required perteachings of the present disclosure or in response to each request fromthe monitoring unit 30.

(d) As reported by the integrated inverter/CC unit 24. The integratedinverter/CC unit 24 may be configured to report the incoming andoutgoing flow numbers for the energy flow to/from the battery 26 to themonitoring unit 30 automatically as required per teachings of thepresent disclosure or in response to each request from the monitoringunit 30.

5. Charge state of the battery 26. The information about the chargestate of the battery 26 may be obtained by the monitoring unit 30 in oneof the following ways:

(a) As reported by the battery unit 26. The battery unit 26 may beconfigured to report its charge state to the monitoring unit 30automatically as required per teachings of the present disclosure or inresponse to each request from the monitoring unit 30.

(b) As reported by a monitoring equipment (not shown) connected to thebattery 26. The monitoring equipment may be operatively connected to themonitoring unit 30—through wired or wireless means—and configured toreport the battery charge state to the monitoring unit 30 automaticallyas required per teachings of the present disclosure or in response toeach request from the monitoring unit 30.

Because the inverter and charge controller are treated as a combinedentity 24 in the present disclosure and because any energy flows betweenthem are ignored, it is observed that, more generally, there may bethree overall energy flows in the system 20 relevant to the discussionof FIG. 3: (i) the unidirectional energy flow from the renewable source22 (for example, solar panels) to the inverter/charge controller (CC)unit 24 as represented by the exemplary arrow 37 in FIG. 3, (ii) thebi-directional energy flow to/from the inverter/CC unit 24 from/to themain AC service panel 28 as represented by the exemplary arrow 38 inFIG. 3, and (iii) the bi-directional energy flow to/from the inverter/CCunit 24 from/to the battery unit 26 as represented by the exemplaryarrow 39 in FIG. 3.

For the system 20 in FIG. 3, the discussion below now addresses indetail two aspects of the present disclosure: (i) production measurementof renewable source in a storage-independent manner, and (ii)calculation of the system storage efficiency. A similar discussion forthe systems in FIGS. 5 and 7 is provided later as well.

I-A. Renewable Source Production Measurement During a Set Interval.

As mentioned before, energy flow information may be conveyed to themonitoring unit 30 either by installing dedicated AC or DC sub-meteringequipment or through metering and information-sharing features builtinto the units 22, 24, 26, and 28 in the system 20. In one embodiment,the monitoring unit 30 may take “snapshots” of the net energy flows atarrows 37-39 at a pre-determined interval such as, for example, every 5minutes or every 15 minutes. The values associated with each snapshotmay be stored in the monitoring unit 30 for further processing as perteachings of the present disclosure. The snapshot interval may be setthrough software programming of the monitoring unit 30. In certainembodiments, the flow-reporting equipment (like a sub-meter) or unit 22,24, 26, 28 may be configured to measure and report the related flowinformation to the monitoring unit 30 at the set interval.Alternatively, the monitoring unit 30 itself may query eachequipment/unit periodically—at the set interval—for the measured flowvalue. In any event, for every flow-measurement period, the delta (ordifference) between the current and previous snapshots may be calculatedby the monitoring unit 30 to be used as interval-specific energy flows.

FIG. 4A shows an exemplary flowchart 46 illustrating how renewablesource production measurement may be performed in a storage-independentmanner according to one embodiment of the present disclosure. The tasksshown in FIG. 4A relate to the system 20 in FIG. 3. In particularembodiments, various tasks illustrated in FIG. 4A may be performed bythe monitoring unit 30 (FIG. 3). Thus, as noted at block 48 in FIG. 4A,the monitoring unit 30 may determine each of the following three valuesduring a pre-determined time interval: (i) an “S” value, which is theinterval-specific magnitude of a first DC energy flow from the renewableenergy source 22 to an intermediate unit, such as the inverter unit 24(or, in one embodiment, the charge controller portion of the inverterunit 24), in the renewable energy system 20 as noted at block 49 (ii) an“M” value, which is the interval-specific magnitude of the AC energyflow between the inverter unit 24 (or, in one embodiment, the inverterportion of the inverter unit 24) and an AC interconnect point 28 in thesystem 20 as noted at block 50; and (iii) a “B” value, which is theinterval-specific magnitude of a second DC energy flow between theinverter unit 24 (or, in one embodiment, the inverter portion of theinverter unit 24) and the DC storage unit 26 in the system 20 as notedat block 51. Just for the sake of illustration, each of these S, M, andB values is shown in FIG. 3 as a dotted, circled letter 42-44 placedover the respective energy flow-indicating arrow 37-39 to indicate theinterval-based measurement and analysis of the associated energy flow asper teachings of the present disclosure.

Furthermore, as discussed in more detail below and as noted at block 52in FIG. 4A, the monitoring unit 30 may use the S, M, and B values tocalculate a portion of the interval-specific AC energy flow attributableonly to the interval-specific first DC energy flow from the renewableenergy source 22, thereby excluding contribution to the AC energy flowfrom the DC storage unit 26. In certain embodiments, the monitoring unit30 also may generate pricing for the interval-specific DC energy flowfrom the renewable energy source 22 in a storage-independent manner—thatis, based on the calculated portion of the interval-specific AC energyflow.

The following energy flow scenarios during a pre-determined measurementtime interval may dictate how the monitoring unit 30 uses the S, M, andB values to determine the interval-specific AC energy flow in astorage-independent manner:

1. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net discharging, and the net energy flow from the inverterunit 24 to the AC main service panel 28 is positive. In this case, theAC energy from the inverter unit 24 results from a sum of S+B, so themonitoring unit 30 may need to allocate a portion of the AC energy to“S.” Thus, in this case, the monitoring unit 30 may calculate (ordetermine) the interval-specific AC energy attributed only to therenewable source—that is, the DC energy flow from the renewable energysource 22—as the ratio M*S/(S+B).

2. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net charging, and the net energy flow from the inverter unit24 to the AC main service panel 28 is positive. In this case, the ACenergy from the inverter unit 24 results from (S−B), so the monitoringunit 30 may calculate (or determine) the interval-specific AC energyattributed only to the renewable source as the ratio M*S/(S−B).

3. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net charging, and the net energy flow from the inverter unit24 to the AC main service panel 28 is negative. In this case, thebattery charge operation is consuming more energy than the solar panel(energy source) 22 is able to provide and, hence, the inverter may bedrawing energy from the AC grid/service point 28 to charge the battery.Thus, the AC energy flow is now resulting from (B−S) and is negative,whereas the actual AC flow could have resulted from “S” and would havebeen positive had the inverter not been drawing energy from the AC grid.However, it is observed that, in this case, the inverter unit 24 is netconverting AC energy to DC. Therefore, the ratio of M to (B−S) may notbe a good multiplier to convert the actual renewable energy (such as thesolar energy) to what the expected AC output would have been. Hence, inthis case, the monitoring unit 30 may multiply the calculation with aninverter roundtrip efficiency factor for the inverter unit 24 to accountfor the negative AC energy flow. (The discussion below addresses how todetermine the inverter efficiency.) Consequently, the monitoring unit 30may calculate the magnitude of the interval-specific AC energyattributed only to the renewable energy (such as the solar energy) asthe ratio M*Eff_(I)*S/(B−S), where “Eff_(I)” is the inverter roundtripefficiency factor. It is noted here that, in some embodiments, the term“Eff_(I)” may indicate a product of the parameters “Eff_(IAC-DC)” and“Eff_(IDC-AC)” discussed later below.

4. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, but the batteryunit 26 is idle. In this case, the monitoring unit 30 may directlyattribute all of the interval-specific AC energy to theinterval-specific renewable energy without any calculations.

5. During the measurement time interval, it may be possible that theenergy source 22 is not generating the renewable energy; the batteryunit 26 may be idle or charging or discharging. In a PV solar systemlike that shown in FIG. 1, there is usually some standby inverterconsumption, which can be allocated to solar (renewable source).However, in an integrated system like that shown in FIG. 3, it may notbe possible to allocate part of any energy consumption by the inverterunit 24 in such a situation to a renewable source. Hence, in this case,the monitoring unit 30 may not allocate any AC energy flow (from theinverter unit 24) to the renewable energy when the source is notgenerating.

In one embodiment, an equivalent comparable AC energy reading for a PVsolar system, such as the system 20 in FIG. 3, from an interval-specificDC solar energy may be obtained by the monitoring unit 30 by directlymultiplying the DC interval energy with an efficiency value (Eff_(I))for the inverter (not shown) in the inverter unit 24.

In certain embodiments, the inverter efficiency (Eff_(I)) may bedetermined or estimated using one of the following two methods:

1. The inverter efficiency curves are well-documented. A nominalefficiency value—which may be referred to as “Eff_(I)”—can be selectedfrom such curves to represent the average operational region of theinverter unit 24 in the renewable energy system 20. The monitoring unit30 may be programmed with this efficiency value (Eff_(I)).

2. In one embodiment, the inverter efficiency value (Eff_(I)) may beestimated using a set of S, M, and B values. For example, if the system20 has the ability to monitor the in/out flow of energy to/from thebattery unit 26 at any given time, the monitoring unit 30 can estimateinverter efficiency (Eff_(I)) by dividing the observed total AC output(from the inverter unit 24) by the observed total DC input (to theinverter unit 24) from the renewable source (that is, from the DC energysource 22) during a time interval when the net battery flow is zero.Thus, the inverter efficiency may be given by Eff_(I)=M/S (when B=0).

By performing the calculations discussed above—starting with thediscussion of FIG. 4A—and recording representative renewable DC energygeneration in AC output terms during a set interval, certain data may begenerated by the monitoring unit 30. In one embodiment, this data may beused, for example, by the monitoring unit 30, for accurate stand-aloneDC energy (for example, solar) billing, independent of storage. Inanother embodiment, this data also may be used by the monitoring unit 30to create analytics of system operations and performance. These aspects(which are also applicable to the embodiments in FIGS. 5-8) areelaborated in more detail below:

1. Standalone Solar Billing: A system may be configured and sold as asolar system by provider A on a Power Purchase Agreement (PPA). Thissystem also may be coupled to an energy storage system by provider B. Incase of such a storage-based PV solar system, the generated DC solarenergy may get split between the fraction that gets diverted to energystorage to charge batteries and the rest which would flow to the ACgrid/load. In this system, billing based on DC alone may be incorrectbecause it would exclude inverter efficiency. On the other hand, billingbased on net AC would also be incorrect because it would exclude storageoperations. However, an interval-based calculation of solar (DC) energyin AC terms as discussed before in the context of the embodiments inFIGS. 3 and 4 “links” the DC source with the AC part of the system andmay serve as an appropriate data for billing because it captures whatthe PV solar system would have delivered to the AC side in the absenceof storage. This may be especially important when energy prices varybased on Time of Use (TOU) pricing, and knowing accurate time intervaldata—such as, for example, the interval-specific S, M, and B valuesdiscussed before—may impact the contracted energy prices in the PPA.

2. Operations and Maintenance (O&M): Some O&M activities in a PV solarsystem may rely on time interval data obtained as per teachings of thepresent disclosure to diagnose gradual declines in performance—such as,for example, increases in shading and/or soiling of a PV panel—versusequipment outages. The interval-specific S, M, and B values generated asdiscussed before may enable this type of O&M activity in the system.

3. Performance Analytics: One possible form of performance analytics ofa PV solar system may use time interval data of solar irradiance asinput and model the expected AC output to actual observed AC output. TheDC output from the PV panels may not be comparable to the AC outputmeasurements obtained from a PV-only system (which is a PV solar systemwithout storage), and may also miss out on some of the modeled causes ofdegraded performance such as, for example, inverter clipping (of ACoutput). On the other hand, the interval-based data measurementsdiscussed above may offer a good substitute to overcome theselimitations.

I-B. Deriving System Storage Efficiency.

The roundtrip storage efficiency number may express the efficiency ofputting a unit of energy into storage and then getting it back. However,system storage efficiency in a renewable energy system with storage maynot simply be the roundtrip efficiency of energy storage; it may be ameasure of what percentage of energy that could have made it out touseful form if the system did not have storage, actually did so in thepresence of storage. For example, if a 5 kW PV system without storagegenerated 600 kWh of AC energy is compared with a first identical systemwith storage that charged and discharged the batteries everyday anddelivered 480 kWh of AC energy, and with a second identical system withstorage that charged and discharged the batteries weekly and delivered540 kWh of AC energy (in both the first and the second systems, it isassumed that the charge state of the battery at the end of the month isidentical to that at the beginning of the month), the storage efficiencyof the first system is 80% and that of the second system is 90%.

In determining system storage efficiency as per particular embodimentsof the present disclosure, two variables of the combination of renewableand storage system may be considered. The first variable is whether theinverter unit 24 allows charging of the energy storage system 26 fromthe AC grid (via the AC interconnect point 28)—that is, whether theinverter (in the inverter unit 24) converts AC to DC for the expresspurpose of charging the batteries in the storage unit 26. The secondvariable is whether the available energy flow data in the renewableenergy system 20 includes disaggregated (directional) flows in eachdirection for energy flow into and out of the battery and between thegrid and the inverter (in the unit 24).

In the discussion below, the terms like “storage efficiency”, “systemstorage efficiency,” and “energy system storage efficiency” are usedinterchangeably to refer to the overall efficiency of the storage unit26 and its operation. In other words, the storage efficiency derivedbelow is more than the efficiency of simply the storage unit 26; thestorage efficiency reflects the efficiency of the storage unit 26 aswell as how it is operated because the strategy of how the storage unit26 is used also affects the operational efficiency of the system 20.

FIG. 4B depicts an exemplary flowchart 53 illustrating how overallefficiency of a DC storage unit, such as the battery unit 26 in FIG. 3,may be measured in a renewable energy system, such as the system 20,according to one embodiment of the present disclosure. In particularembodiments, various tasks illustrated in FIG. 4B may be performed bythe monitoring unit 30 (FIG. 3). As noted at block 54-1, the monitoringunit 30 may determine a sum of “S” values. Each S value in the sum isassociated with a corresponding one of a plurality of pre-determinedtime intervals and is an interval-specific magnitude of a DC energy flowfrom a renewable energy source, such as the source 22, to an inverter(like the inverter in the inverter unit 24) in the system 20. As shownin FIG. 3, the DC storage unit 26 may be operatively connected to theinverter and configured to store DC energy. At block 54-2, themonitoring unit 30 may further determine a sum of “M” values. Each Mvalue in the sum is associated with a corresponding one of the pluralityof pre-determined time intervals and is an interval-specific magnitudeof an AC energy flow between the inverter (in the inverter unit 24) andan AC interconnect point (such as the mains panel 28) in the system 20.Thereafter, at block 54-3, the monitoring unit 30 may use the sum of Svalues (determined at block 54-1), the sum of M values (determined atblock 54-2), and an efficiency factor for the inverter (in the inverterunit 24) to calculate the overall efficiency of the DC storage unit 26and operation thereof. Various operational cases described below provideadditional details of the tasks shown in FIG. 4B.

Case 1: Inverter Cannot Charge Energy Storage from Grid Power (that is,No AC to Dc Conversion).

In this case, although the DC renewable energy from the source 22 may gointo the battery 26 (via the inverter unit 24), eventually the sum ofall outflows (M) from the inverter unit 24 may have their originalsource in the sum of all inflows (S) from the renewable source 22.Therefore, to determine the overall efficiency of the energy storagesystem 26 that can be attributed to the round-trip battery transfers(that is, energy flow to and from the battery, including multipletimes), it may be preferable to isolate and remove the impact ofinverter efficiency. As discussed before, in certain embodiments, theinverter efficiency (Eff_(I)) may be determined or estimated using oneof the following two methods:

1. The inverter efficiency curves are well-documented. A nominalefficiency value—which may be referred to as “Eff_(I)”—can be selectedfrom such curves to represent the average operational region of theinverter (not shown) in the inverter unit 24 in the renewable energysystem 20. The monitoring unit 30 may be programmed with this efficiencyvalue (Eff_(I)).

2. In one embodiment, the inverter efficiency value (Eff_(I)) may beestimated using a set of S, M, and B values. For example, if the system20 has the ability to monitor the in/out flow of energy to/from thebattery unit 26 at any given time, the monitoring unit 30 can estimateinverter efficiency (Eff_(I)) by dividing the observed AC output (fromthe inverter unit 24) by the observed DC input (to the inverter unit 24)from the renewable source (that is, from the DC energy source 22) duringa time interval when the net battery flow is zero. Thus, the inverterefficiency may be given by Eff_(I)=M/S (when B=0).

In this case under consideration, the relationship between M and S overa long term may be given by:Sum(M)=Sum(S)*(storage efficiency)*(Eff_(I))+(change in stored batteryenergy)*(Eff_(I))  (1)

In the equation (1) above, the parameter “Sum(M)” refers to the sum of aplurality of M values, each M value being associated with acorresponding measurement time interval as discussed before. Similarly,the parameter “Sum(S)” refers to the sum of a plurality of S valuesdetermined over a corresponding plurality of measurement intervals.Furthermore, it is noted that the parameter referred to as “change instored battery energy” in equation (1) should be multiplied with thebattery's discharging efficiency if the parameter is negative anddivided by the battery's charging efficiency if the parameter ispositive. However, these efficiencies are not mentioned in equation (1)above because the delta (difference) in the stored energy is negligibleenough over a long period of time and charging and dischargingefficiencies may be close enough to “1”.

From equation (1), the overall storage efficiency—that is, efficiency ofthe system that can be attributed to battery storage, charge, anddischarge cycles—can be given as:Storage efficiency=(Sum(M)−(change in stored batteryenergy)*Eff_(I))/(Sum(S)*Eff_(I))  (2)

In the equation (2) above, the known or estimated inverter efficiency(Eff_(I)) (as discussed before) can be substituted. Furthermore, whenenergy storage system efficiency in equation (2) is evaluated over along period of time, such as, for example, over months or years, changesin energy storage level may become insignificant. In that case, equation(2) may be simplified to:Energy storage system efficiency=Sum(M)/(Sum(S)*Eff_(I))  (3)

In particular embodiments, the monitoring unit 30 may be programmed touse the equation (3) above to determine overall efficiency of the energystorage unit 26 and how it is operated, and the impact of the storageefficiency for the system as a whole.

Case 2: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows for Mare Available.

In this case, the term “M_(out)” (associated with a measurementinterval) may be used to represent the interval-specific magnitude ofthe AC energy flow M from the inverter (not shown) in the inverter unit24 into the AC interconnect point 28. Similarly, the term “M_(in)”(associated with the same or another measurement interval) may be usedto represent the interval-specific magnitude of the AC energy flow Mfrom the AC interconnect point 28 into the inverter in the inverter unit24. Consequently, the relationship between M (which includes M_(out) aswell as M_(in)) and S over a long term may be given by:Sum(M _(out))=Sum(S)*(Eff_(IDC-AC))*(storage efficiency)+Sum(M_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))*(storage efficiency)+(change instored battery energy)*(Eff_(IDC-AC))  (4)

In the equation (4) above, the parameter “Sum(M_(out))” refers to thesum of a plurality of M_(out) values, each M_(out) value beingassociated with a corresponding measurement time interval as discussedbefore. Similarly, the parameter “Sum(M_(in))” refers to the sum of aplurality of M_(in) values, each M_(in) value being associated with acorresponding measurement time interval as discussed before. In oneembodiment, the same measurement interval may have both M_(out) as wellas M_(in) values depending on the direction of the AC energy flow for M.The parameter “Sum(S)” refers to the sum of a plurality of S valuesdetermined over a corresponding plurality of measurement intervals. Theparameters “Eff_(IAC-DC)” and “Eff_(IDC-AC)” in equation (4) arediscussed later below. Furthermore, it is noted that the parameterreferred to as “change in stored battery energy” in equation (4) shouldbe multiplied with the battery's discharging efficiency if the parameteris negative and divided by the battery's charging efficiency if theparameter is positive. However, these efficiencies are not mentioned inequation (4) above because the delta (difference) in the stored energyis negligible enough over a long period of time and charging anddischarging efficiencies may be close enough to “1”.

From equation (4), the overall storage efficiency—that is, efficiency ofthe system that can be attributed to battery storage, charge, anddischarge cycles—can be given as:Storage efficiency=[Sum(M _(out))−(change in stored batteryenergy)*(Eff_(IDC-AC)]/[Sum(S)*(Eff_(IDC-AC))+Sum(M_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))]  (5)

When energy storage system efficiency in equation (5) is evaluated overlong timeframes, such as, for example, over months or years, the changein the stored battery energy is insignificant in comparison to otherenergy flows in equation (5) and, hence, it can be ignored. In thatcase, equation (5) may be simplified to:Storage efficiency=Sum(M _(out))/[Sum(S)*(Eff_(IDC-AC))+Sum(M_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))]  (6)

In particular embodiments, the monitoring unit 30 may be programmed touse the equation (6) above to determine efficiency of the energystorage, such as the storage unit 26 in FIG. 3, and the impact of thestorage efficiency for the system as a whole.

In the equations (4)-(6) above, the parameter “Eff_(IDC-AC)” is theDC-to-AC conversion efficiency of the inverter (not shown) in theinverter unit 24, and the parameter “Eff_(IAC-DC)” is the AC-to-DCconversion efficiency of the inverter. Like the known or estimatedinverter efficiency (Eff_(I)) discussed before, the inverterefficiencies Eff_(IAC-DC) and Eff_(IDC-AC) also may be obtained orestimated as follows:

1. Nominal values for inverter-specific Eff_(IAC-DC) and Eff_(IDC-AC)may be obtained from the known inverter efficiency curves.

2. In one embodiment, when disaggregated flows for B are available inthe form of the parameters “B_(in)” (energy flow into the storage unit26) and “B_(out)” (energy flow out of the storage unit 26), then theratio M_(out)/S may be used by the monitoring unit 30 during a timeinterval when B_(in)=0 and B_(out)=0 to estimate the efficiencyEff_(IDC-AC). On the other hand, during a time interval when S=0,B_(out)=0, and B_(in) is positive, the monitoring unit 30 may use theratio B_(in)/M_(in) to estimate the efficiency Eff_(IAC-DC).

The values of Eff_(IAC-DC) and Eff_(IDC-AC) obtained or estimated asnoted above can be substituted in equation (6) to determine the overallstorage efficiency and its impact for the system as a whole.

Case 3: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows for Band M are not Available.

When disaggregated (directional) flows are not available, short timeinterval based sampling may be used by the monitoring unit 30 todetermine B and M values, while assuming that the flow direction for Band M are constant within the given time interval. Based on thisassumption, measured values may be added by the monitoring unit 30 intoseparate “buckets” (like a storage memory location or register) based ondirection so that the approach presented in this case can be used. Forexample, if “B_(in)” is the battery inflow during a short time intervalsuch as, for example, 5 minutes, its magnitude may be added to aregister designated as a “B_(in) register”. Similarly, if “B_(out)” isthe battery outflow during a short 5-minute time interval, its magnitudemay be added to a register designated as a “B_(out) register”. For M, ifthe 5 minute interval energy flow is from the grid to the inverter, itmay be added to a register designated as an “M_(in) register,” and ifthe 5 minute interval energy flow is from the inverter to the grid, itmay be added to a register designated as an “M_(out) register.” Theregisters or memory locations may be part of a memory—such as the memory119 in FIG. 9—in the monitoring unit 30. The monitoring unit 30 may thenuse equation (6) with the disaggregated values of B and M determined bythe monitoring unit 30 based on short time interval sampling tocalculate the overall efficiency of the storage unit 26 and itsoperation, and the impact of the storage efficiency for the system as awhole.

The table below summarizes the processing to be done by the monitoringunit 30 in each of the three cases discussed in Part I-B above:

Inverter can charge battery Inverter cannot charge from grid batteryfrom grid Disaggregated Case 2: Use equation (6) to Case 1: Use equation(3) to flows determine system storage determine storage availableefficiency efficiency Disaggregated Case 3: Disaggregate flows Case 1:Use equation (3) to flows not by short time interval determine storageavailable sampling, then use equation efficiency (6) to determinestorage efficiencyII. DC-Coupled System with Critical and Auxiliary Loads

FIG. 5 is a simplified block diagram of a DC coupled renewable energysystem 55 (with critical and auxiliary loads) according to oneembodiment of the present disclosure showing various energy flows to bemeasured on a per-interval basis as per teachings of the presentdisclosure for calculations of renewable source production and systemstorage efficiency. It is noted here that although the systems in FIGS.5 and 7 are different from each other and different from the system 20in FIG. 3, for the sake of consistency and ease of discussion, the samereference numerals are used in FIGS. 3, 5, and 7 for systementities/units having the same or similar functionalities. Furthermore,also for the sake of consistency and ease of discussion, the samereference numeral “30” is used in FIGS. 3, 5, and 7 to refer to themonitoring unit generally. It is understood, however, that a monitoringunit designed to operate with one system may need to be modified (inhardware and/or software) to operate in the other because of differentenergy flows to be measured and different calculations to be performed,as discussed in more detail below.

For the sake of brevity, the earlier discussion of components/units andenergy flows common between FIGS. 3, 5, and 7 is not repeated here.Furthermore, the earlier-provided ancillary discussion (such as, forexample, IP or packet network based connections to the monitoring unit30, different ways to measure and report energy flows, and the like)related to such components and energy flows is also not repeated herefor the sake of brevity. However, it is understood that all suchdiscussion—whether repeated here or not—remains applicable to theembodiments in FIGS. 5 and 7 to the extent relevant. The discussionbelow, therefore, primarily focuses on the distinctive aspects of FIGS.5 and 7.

In addition to the components/units and energy flows shown in FIG. 3,the system 55 in FIG. 5 also includes a critical loads panel 57 and anauxiliary (Aux) loads panel 59. The critical loads panel 57 may supplyAC energy to various critical loads, and the aux loads panel 59 maysupply AC energy to certain auxiliary loads. A critical load may besomething that should have backup power in case of a power outage suchas, for example, a refrigerator or basic lighting in a home. On theother hand, an auxiliary load preferably may be powered fromrenewables/battery when excess energy is available and may never drawand pay for the grid power, or may be powered based on some other rulesas to when it is permissible to provide power to an auxiliary load. Forexample, a pool heater or an electric car charger in a home may beconsidered auxiliary loads. In FIGS. 5 and 7, the AC serviceinterconnect point 28 is referred to simply as a “Mains Panel” throughwhich AC power (from the inverter unit 24) may be provided to an AC grid(not shown) or AC power from the grid may be supplied to the inverterunit 24 (for example, to power the Aux and critical loads). In certainembodiments, energy flow metering may be integral to the critical loadspanel 57 and/or the Aux loads panel 59, which may be configured to beoperatively connected with the monitoring unit 30 to perform meteringand reporting of relevant energy flow measurements to the monitoringunit 30 via their respective connections (shown by dotted arrows 61,62)—direct or indirect (such as through a network). Like the connections32-35, one or more of the connections 61-62 may be wired or wireless,and may be via a communication network such as the Internet.

Because the inverter and charge controller are treated as a combinedentity 24 in the present disclosure and because any energy flows betweenthem are ignored, it is observed that, more generally, there may be fiveoverall energy flows in the system 55 relevant to the discussion of FIG.5: (i) the unidirectional DC energy flow from the renewable source 22(for example, solar panels) to the inverter/charge controller (CC) unit24 as represented by the exemplary arrow 37 in FIG. 5, (ii) thebi-directional AC energy flow to/from the inverter/CC unit 24 from/tothe mains panel 28 as represented by the exemplary arrow 38 in FIG. 5,(iii) the bi-directional DC energy flow to/from the inverter/CC unit 24from/to the battery unit 26 as represented by the exemplary arrow 39 inFIG. 5, (iv) the unidirectional AC energy flow from the inverter unit 24to the critical loads panel 57 as represented by the exemplary arrow 64in FIG. 5, and (v) the unidirectional AC energy flow from the inverterunit 24 to the Aux loads panel 59 as represented by the exemplary arrow65 in FIG. 5. In some embodiments, the AC energy flows 38 and 64-65 mayprimarily involve the inverter (not shown) in the inverter unit 24.

In FIG. 5, the inverter (in the inverter unit 24) may serve threefunctions:

(i) It can output AC energy to three different AC connections 28, 57,59, separately.

(ii) It can act as a switch that connects the AC grid power from themains panel 28 through it to the critical loads panel 57 and the auxloads panel 59.

(iii) It can act as a switch that disconnects the mains panel 28 fromthe critical loads panel 57 and/or the aux loads panel 59 in case of agrid outage so that it can power these loads, if required, fromrenewables 22 or the battery 26 without islanding risk.

For the system 55 in FIG. 5, the discussion below now addresses indetail two aspects of the present disclosure: (i) production measurementof renewable source in a storage-independent manner, and (ii)calculation of the system storage efficiency.

II-A. Renewable Source Production Measurement During a Set Interval.

As mentioned before, energy flow information may be conveyed to themonitoring unit 30 either by installing dedicated AC or DC sub-meteringequipment or through metering and information-sharing features builtinto the units 22, 24, 26, 28, 57, and 59 in the system 55. In oneembodiment, the monitoring unit 30 may take “snapshots” of the netenergy flows at arrows 37-39 and 64-65 at a pre-determined interval suchas, for example, every 5 minutes or every 15 minutes. The valuesassociated with each snapshot may be stored in the monitoring unit 30for further processing as per teachings of the present disclosure. Thesnapshot interval may be set through software programming of themonitoring unit 30. In certain embodiments, the flow-reporting equipment(like a sub-meter) or unit 22, 24, 26, 28, 57, and 59 may be configuredto measure and report the related flow information to the monitoringunit 30 at the set interval. Alternatively, the monitoring unit 30itself may query each equipment/unit periodically—at the setinterval—for the measured flow value. In any event, for everyflow-measurement period, the delta (or difference) between the currentand previous snapshots may be calculated by the monitoring unit 30 to beused as interval-specific energy flows.

FIG. 6A shows an exemplary flowchart 70 illustrating how renewablesource production measurement may be performed in the system 55 of FIG.5 in a storage-independent manner according to one embodiment of thepresent disclosure. In particular embodiments, various tasks illustratedin FIG. 6A may be performed by the monitoring unit 30 (FIG. 5). Thus, asnoted at block 72 in FIG. 6A, the monitoring unit 30 may determine eachof the following five values during a pre-determined time interval: (i)an “S” value, which is the interval-specific magnitude of a first DCenergy flow from the renewable energy source 22 to an intermediate unit,such as the inverter unit 24 (or, in one embodiment, the chargecontroller portion of the inverter unit 24), in the renewable energysystem 55 as noted at block 73; (ii) an “M” value, which is theinterval-specific magnitude of the first AC energy flow between theintermediate unit 24 (or, in one embodiment, the inverter portion of theinverter unit 24) and an AC interconnect point (or Mains Panel) 28 inthe system 55 as noted at block 74; (iii) a “C” value, which is theinterval-specific magnitude of a second AC energy flow from the inverterunit 24 (or, in one embodiment, the inverter portion of the inverterunit 24) to a critical loads panel 57 in the system 55 as noted at block75; (iv) an “A” value, which is the interval-specific magnitude of athird AC energy flow from the intermediate unit 24 (or, in oneembodiment, the inverter portion of the inverter unit 24) to anauxiliary loads panel 59 in the system 55 as noted at block 76, and (v)a “B” value, which is the interval-specific magnitude of a second DCenergy flow between the inverter unit 24 (or, in one embodiment, theinverter portion of the inverter unit 24) and the DC storage unit 26 inthe system 55 as noted at block 77. Just for the sake of illustration,each of these S, M, C, A, and B values is shown in FIG. 5 as a dotted,circled letter 42-44 and 67-68 placed over the respective energyflow-indicating arrow 37-39 and 64-65 to indicate the interval-basedmeasurement and analysis of the associated energy flow as per teachingsof the present disclosure.

As noted at block 79 in FIG. 6A and discussed in more detail below, themonitoring unit 30 may determine an interval-specific net AC energy flowout of the intermediate unit 24 based on a directional summation of theM, C, and A values. Furthermore, as also discussed in more detail belowand as noted at block 81 in FIG. 6A, the monitoring unit 30 may use theS, M, C, A, and B values to calculate a portion of the interval-specificnet AC energy flow (determined at block 79) attributable only to theinterval-specific first DC energy flow from the renewable energy source22, thereby excluding contribution to the net AC energy flow from the DCstorage unit 26. In certain embodiments, the monitoring unit 30 also maygenerate pricing for the interval-specific DC energy flow from therenewable energy source 22 in a storage-independent manner—that is,based on the calculated portion of the interval-specific net AC energyflow.

Unlike the M value in the context of FIGS. 3-4, the M, C, and A valuesin the context of FIGS. 5-6 may be defined as signed numbers. Thus, thefollowing may apply in the context of FIGS. 5-6:

(i) The M value may be measured in the direction away from the inverterunit 24. In other words, the M value may be positive when the AC energyis flowing from the inverter unit 24 to the mains panel 28, and negativewhen it is flowing from the mains panel 28 to the inverter unit 24.

(ii) The C value also may be measured in the direction away from theinverter unit 24. In other words, the C value may be positive when ACenergy is flowing from the inverter unit 24 to the critical loads panel57, and negative when it is flowing from the critical loads panel 57 tothe inverter unit 24. Unless a second energy source is connected up tothe critical loads panel 57 that can feed power into the panel 57, thisflow will always be positive—as indicated by the unidirectional arrow64.

(iii) The A value also may be measured in the direction away from theinverter unit 24. In other words, the A value may be positive when ACenergy is flowing from the inverter unit 24 to the Aux loads panel 59,and negative when it is flowing from the Aux loads panel 59 to theinverter unit 24. Unless a second energy source is connected up to theaux loads panel 59 that can feed power into the panel 59, this flow willalways be positive—as indicated by the unidirectional arrow 65.

It is noted here that, in some embodiments, the aux loads panel 59 andthe inverter unit's 24 connection to it may be optional and may simplynot exist. In that case, the A value may not exist and, hence, the Avalue be treated as zero in various equations given below.

Because the M, C, and A values are defined as signed numbers in thecontext of the embodiments in FIGS. 5-6, the net value of AC energy flowinto/out of the inverter unit 24 may be calculated before the magnitudeof this net value is determined. Thus, any critical or aux loads beingfed from the mains panel 28 can be cancelled out. In the discussion ofFIGS. 5-6, the expression “(M+C+A)” may refer to the magnitude of theinterval-specific net AC energy flow into/out of the inverter unit 24based on a directional summation of the M, C, and A values—a value willbe positive when its associated AC flow is out of the inverter unit 24and negative when its associated AC flow is into the inverter unit 24,as noted above. As mentioned below, the net AC flow in the directionaway from the inverter unit 24 may be more relevant for renewablesproduction measurement in a storage-independent manner. Hence, inparticular embodiments, the expression “(M+C+A)” may primarily refer tothe interval-specific net AC energy flow out of the inverter unit 24 asa summation of the signed M, A, and C values.

For renewables production measurement during a set interval, theparameter “M” in various calculations in Part I-A above may be replacedby “M+C+A” where all three flows are measured in the direction goingaway from the inverter unit 24. Setting this direction of measurementmay allow the summation to cancel out any part of critical loads or auxloads being supplied directly from the mains panel 28. For example, ifthe critical loads are drawing 100 Wh (watt-hour) from the inverter unit24 during the interval (a positive “C” value of 100 Wh), the aux loadsare drawing 400 Wh from the inverter unit 24 during the same interval (apositive “A” value of 400 Wh), and the mains energy flow is supplying300 Wh to the inverter unit 24 during the interval (a negative “M” valueof 300 Wh), then summing these flows in the direction away from theinverter would give 400+100−300=200 Wh (which are coming from theinverter in the inverter unit 24). On the other hand, if the mains issupplying 600 Wh, then the sum would yield 400+100−600=(−100 Wh), whichindicates that the inverter unit 24 is drawing 100 Wh from the AC side(for example, from the AC grid connected to the mains panel 28) tocharge the battery 26 in addition to what it is using from the renewableDC source 22. Thus, it is observed that the sum (M+C+A) in the directionaway from the inverter unit 24 may provide a measurement of the netenergy flow resulting from the PV array 22 and/or the storage unit 26during any interval, and hence can replace the parameter “M” in variouscalculations in part I-A above, as given below.

The following energy flow scenarios during a pre-determined measurementtime interval may dictate how the monitoring unit 30 uses the S, M, C,A, and B values to determine the interval-specific AC energy flow in astorage-independent manner:

1. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net discharging, and the net AC energy output from theinverter unit 24 is positive. In this case, the AC energy from theinverter unit 24 results from a sum of S+B, so the monitoring unit 30may need to allocate a portion of the AC energy to “S.” Thus, in thiscase, the monitoring unit 30 may calculate (or determine) theinterval-specific AC energy attributed only to the renewable source—thatis, the DC energy flow from the renewable energy source 22—as the ratio(M+C+A)*S/(S+B).

2. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net charging, and the net AC energy flow from the inverterunit 24 is positive. In this case, the AC energy from the inverter unit24 results from (S−B), so the monitoring unit 30 may calculate (ordetermine) the interval-specific AC energy attributed only to therenewable source as the ratio (M+C+A)*S/(S−B).

3. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, the batteryunit 26 is net charging, and the net AC energy flow from the inverterunit 24 is negative. In this case, the battery charge operation isconsuming more energy than the solar panel (energy source) 22 is able toprovide and, hence, the inverter may be drawing energy from the ACgrid/service point 28 to charge the battery. Thus, the AC energy flow isnow resulting from (B−S) and is negative, whereas the actual AC flowcould have resulted from “S” and would have been positive had theinverter not been drawing energy from the AC grid. However, it isobserved that, in this case, the inverter unit 24 is net converting ACenergy to DC. Therefore, the ratio of M to (B−S) may not be a goodmultiplier to convert the actual renewable energy (such as the solarenergy) to what the expected AC output would have been. Hence, in thiscase, the monitoring unit 30 may multiply the calculation with aninverter roundtrip efficiency factor for the inverter unit 24 to accountfor the negative AC energy flow. (The discussion below addresses how todetermine the inverter efficiency.) Consequently, the monitoring unit 30may calculate the magnitude of the interval-specific AC energyattributed only to the renewable energy (such as the solar energy) asthe ratio −1*(M+C+A)*Eff_(I)*S/(B−S), where “Eff_(I)” is the inverterroundtrip efficiency factor. In some embodiments, the term “Eff_(I)” mayindicate a product of the parameters “Eff_(IAC-DC)” and “Eff_(IDC-AC)”mentioned before. The “−1” value in this ratio compensates for the factthat the current net flow is negative, but would have been positivewithout storage in the picture.

4. During the measurement time interval, it may be possible that theenergy source 22 is net generating the renewable energy, but the batteryunit 26 is idle. In this case, the monitoring unit 30 may directlyattribute all of the interval-specific AC energy to theinterval-specific renewable energy without any calculations.

5. During the measurement time interval, it may be possible that theenergy source 22 is not generating the renewable energy; the batteryunit 26 may be idle or charging or discharging. In a PV solar systemlike that shown in FIG. 1, there is usually some standby inverterconsumption, which can be allocated to solar (renewable source).However, in an integrated system like that shown in FIG. 5 (whereinverter and charge controller are integrated into one unit 24), it maynot be possible to allocate part of any energy consumption by theinverter unit 24 in such a situation to a renewable source. Hence, inthis case, the monitoring unit 30 may not allocate any AC energy flow(from the inverter unit 24) to the renewable energy when the source isnot generating.

In one embodiment, an equivalent comparable AC energy reading for a PVsolar system, such as the system 20 in FIG. 3, from an interval-specificDC solar energy may be obtained by the monitoring unit 30 by directlymultiplying the DC interval energy with an efficiency value (Eff_(I))for the inverter (not shown) in the inverter unit 24.

In certain embodiments, the inverter efficiency (Eff_(I)) may bedetermined or estimated using one of the following two methods:

1. The inverter efficiency curves are well-documented. A nominalefficiency value—which may be referred to as “Eff_(I)”—can be selectedfrom such curves to represent the average operational region of theinverter unit 24 in the renewable energy system 55. The monitoring unit30 may be programmed with this efficiency value (Eff_(I)).

2. In one embodiment, the inverter efficiency value (Eff_(I)) may beestimated using a set of S, M, and B values. For example, if the system55 has the ability to monitor the in/out flow of energy to/from thebattery unit 26 at any given time, the monitoring unit 30 can estimateinverter efficiency (Eff_(I)) by dividing the observed total AC outputto the mains panel 28 (from the inverter unit 24) by the observed totalDC input (to the inverter unit 24) from the renewable source (that is,from the DC energy source 22) during a time interval when the netbattery flow is zero. Thus, the inverter efficiency may be given byEff^(I)=(M+C+A)/S (when B=0).

By performing the calculations discussed above—starting with thediscussion of FIG. 6A—and recording representative renewable DC energygeneration in AC output terms during a set interval, certain data may begenerated by the monitoring unit 30. In one embodiment, this data may beused, for example, by the monitoring unit 30, for accurate stand-aloneDC energy (for example, solar) billing, independent of storage. Inanother embodiment, this data also may be used by the monitoring unit 30to create analytics of system operations and performance as discussedearlier under Part I-A.

II-B. Deriving System Storage Efficiency.

The roundtrip storage efficiency number may express the efficiency ofputting a unit of energy into storage and then getting it back. Indetermining system storage efficiency as per particular embodiments ofthe present disclosure, two variables of the combination of renewableand storage system may be considered. The first variable is whether theinverter unit 24 allows charging of the energy storage system 26 fromthe AC grid (via the mains panel 28). The second variable is whether theavailable energy flow data in the renewable energy system 55 includesdisaggregated (directional) flows in each direction for energy flow intoand out of the battery and into and out of the inverter (in the unit24).

FIG. 6B Depicts an exemplary flowchart 82 illustrating how efficiency ofthe DC storage unit 26 in the renewable energy system 55 of FIG. 5 maybe measured according to one embodiment of the present disclosure. Inparticular embodiments, various tasks illustrated in FIG. 6B may beperformed by the monitoring unit 30 (FIG. 5). Thus, as noted at block82-1, the monitoring unit 30 may determine a sum of “S” values. Each Svalue in the sum may be associated with a corresponding one of aplurality of pre-determined time intervals and may be aninterval-specific magnitude of a DC energy flow from a renewable energysource, such as the source 22, to an inverter (such as the inverter inthe inverter unit 24) in the system 55. As noted at block 82-1 and shownin FIG. 5, the DC storage unit 26 may be operatively connected to theinverter and configured to store DC energy. At block 82-2, themonitoring unit 30 may further determine a sum of (M+C+A) values. Each(M+C+A) value in the sum of (M+C+A) values may be associated with acorresponding one of the plurality of pre-determined time intervals andmay include an “M” value, a “C” value, and an “A” value. As noted atblock 82-3, the M value may be an interval-specific magnitude of a firstAC energy flow between the inverter and an AC interconnect point (suchas the mains panel 28) in the system 55. As noted at block 82-4, the Cvalue may be an interval-specific magnitude of a second AC energy flowfrom the inverter to a critical loads panel (such as the panel 57) inthe system 55. Similarly, as noted at block 82-5, the A value may be aninterval-specific magnitude of a third AC energy flow from the inverterto an auxiliary loads panel (such as the panel 59) in the system 55.Thereafter, at block 82-6, the monitoring unit 30 may calculate theefficiency of the DC storage unit 26 using the sum of S values(determined at block 82-1), the sum of (M+C+A) values (determined atblock 82-2), and an efficiency factor for the inverter. Variousoperational cases described below provide additional details of thetasks shown in FIG. 6B.

Case 1: Inverter Cannot Charge Energy Storage from Grid Power (that is,No AC to Dc Conversion).

In this case, although the DC renewable energy from the source 22 may gointo the battery 26 (via the inverter unit 24), eventually the net sumof all AC energy outflows (M+C+A) from the inverter unit 24 may havetheir original source in the sum of all inflows (S) from the renewablesource 22. Therefore, to determine the overall efficiency of the energystorage system 26 that can be attributed to the round-trip batterytransfers (that is, energy flow to and from the battery, includingmultiple times), it may be preferable to isolate and remove the impactof inverter efficiency. As discussed before, in certain embodiments, theinverter efficiency (Eff_(I)) may be determined or estimated using oneof the following two methods:

1. The inverter efficiency curves are well-documented. A nominalefficiency value—which may be referred to as “Eff_(I)”—can be selectedfrom such curves to represent the average operational region of theinverter unit 24 in the renewable energy system 55. The monitoring unit30 may be programmed with this efficiency value (Eff_(I)).

2. In one embodiment, the inverter efficiency value (Eff_(I)) may beestimated using a set of S, M, and B values. For example, if the system55 has the ability to monitor the in/out flow of energy to/from thebattery unit 26 at any given time, the monitoring unit 30 can estimateinverter efficiency (Eff_(I)) by dividing the observed total AC outputto the mains panel 28 (from the inverter unit 24) by the observed totalDC input (to the inverter unit 24) from the renewable source (that is,from the DC energy source 22) during a time interval when the netbattery flow is zero. Thus, the inverter efficiency may be given byEff_(I)=(M+C+A)/S (when B=0).

Because the inverter does not charge batteries 26 from AC energy (fromthe grid) in the instant case, the net M+C+A sum is either zero (no netAC energy output from the inverter) or positive (some AC energy outputfrom the inverter). Hence, the parameter “M” in various calculations inPart I-B (Case 1) above may be replaced by the sum of net (M+C+A) flows.As in case of Part II-A, the M, C, and A values are measured going awayfrom the inverter to exclude the effects from the mains power feedingcritical or aux loads.

In this case under consideration, the relationship among M, C, A, and Sover a long term may be given by:Sum(M+C+A)=Sum(S)*(storage efficiency)*(Eff_(IDC-AC))+(change in storedbattery energy)*(Eff_(IDC-AC))  (7)

In the equation (7) above, the parameter “Sum(M+C+A)” refers to the sumof a plurality of (M+C+A) values, each (M+C+A) value being associatedwith a corresponding measurement time interval as discussed before.Similarly, the parameter “Sum(S)” refers to the sum of a plurality of Svalues determined over a corresponding plurality of measurementintervals. Furthermore, it is noted that the parameter referred to as“change in stored battery energy” in equation (7) should be multipliedwith the battery's discharging efficiency if the parameter is negativeand divided by the battery's charging efficiency if the parameter ispositive. However, these efficiencies are not mentioned in equation (7)above because the delta (difference) in the stored energy is negligibleenough over a long period of time and charging and dischargingefficiencies may be close enough to “1”.

From equation (7), the overall storage efficiency—that is, efficiency ofthe system that can be attributed to battery storage, charge, anddischarge cycles—can be given as:Storage efficiency=(Sum(M+C+A)−(change in stored batteryenergy)*Eff_(I))/(Sum(S)*Eff_(I))   (8)

In the equation (8) above, the parameter “Eff_(I)” is used in place ofthe parameter “Eff_(IDC-AC)” (in equation (7)) because the invertercannot charge the battery from the AC grid power and, hence, DC-to-ACconversion is the only conversion it is capable of. Therefore, theparameter “Eff_(IDC-AC)” in equation (7) may be replaced by the generalparameter “Eff_(I)”. The known or estimated inverter efficiency(Eff_(I)) (as discussed before) can be substituted in equation (8).Furthermore, when energy storage system efficiency in equation (8) isevaluated over a long period of time, such as, for example, over monthsor years, changes in energy storage level may become insignificant. Inthat case, equation (8) may be simplified to:Energy storage system efficiency=Sum(M+C+A)/(Sum(S)*Eff_(I))  (9)

In particular embodiments, the monitoring unit 30 in the renewableenergy system 55 in FIG. 5 may be programmed to use the equation (9)above to determine overall efficiency of the energy storage unit 26 andhow it is operated, and the impact of the storage efficiency for thesystem as a whole.

Case 2: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows forM+C+A are Available.

In this case, the disaggregated flows of M (M_(out) and M_(n)) alone maynot be helpful because, depending on the consumption by critical and auxloads, M can be positive or negative even when the inverter isoutputting AC energy. Therefore, it may be preferable to perform anaggregation of M+C+A when net M+C+A is positive separate from anaggregation of M+C+A when net M+C+A is negative. In particularembodiments, the inverter unit 24 may be configured to provide thisinformation natively because these are just separate sums of its ACoutputs and inflows, which may be recorded (for each measurement timeinterval) into two separate memory locations or registers (not shown) inthe inverter unit 24. The recorded sums of disaggregated energy flows ofM, C, and A may be sent to the monitoring unit 30 to enable it toperform the calculations outlined below.

Here, the term “(M+C+A)_(out)” (associated with a measurement interval)may be used to represent the interval-specific magnitude of the net ACenergy flow out of the inverter (not shown) in the inverter unit 24.Similarly, the term “(M+C+A)_(in)” (associated with the same or anothermeasurement interval) may be used to represent the interval-specificmagnitude of the net AC energy flow into the inverter in the inverterunit 24. Although (M+C+A)_(out) represents net positive energy flow and(M+C+A)_(in) represents the net negative energy flow, each of thesevalues ((M+C+A)_(out) and (M+C+A)_(in)), however, will be recorded aspositive values in two separate memory locations/registers. For example,two energy-metering registers may record positive values—one register(the (M+C+A)_(out) register) incrementing whenever M+C+A is net flowingaway from the inverter, and the other register (the (M+C+A)_(in)register) incrementing only when the net M+C+A is into the inverter. So,over any measurement interval, the interval-specific (M+C+A)_(out) valueis the interval-specific change recorded in the (M+C+A)_(out) register,which can only be positive. Similarly, the interval-specific(M+C+A)_(in) value is the interval-specific change recorded in the(M+C+A)_(in) register, which can only be positive as well. In certainembodiments, the (M+C+A)_(out) and (M+C+A)_(in) values may be obtainedin a different manner—using a pair of separate disaggregated flowregisters for M (the M_(out) and M_(in) registers) along with normalregisters for C and A (because the assumption is that since C and A areloads, they cannot cause energy flow into the inverter). Thus, with anM_(out) register, an M_(in) register, a C register, and an A register,the (M+C+A)_(out) becomes (M_(out)+C+A) and (M+C+A)_(in) becomes justM_(in).

In particular embodiments, the interval-specific net AC energy flows((M+C+A)_(out) and (M+C+A)_(in)) may be to/from the grid (at mains panel28), respectively. Consequently, the relationship between M+C+A (whichincludes (M+C+A)_(out) as well as (M+C+A)_(in)) and S over a long termmay be given by:Sum((M+C+A)_(out))=Sum(S)*(Eff_(IDC-AC))*(storageefficiency)+Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(EFF_(IDC-AC))*(storageefficiency)+(change in stored battery energy)*(Eff_(IDC-AC))  (10)

In the equation (10) above, the parameter “Sum((M+C+A)_(out))” refers tothe sum of a plurality of (M+C+A)_(out) values, each (M+C+A)_(out) valuemay be a positive value and may be associated with a correspondingmeasurement time interval as discussed before. Similarly, the parameter“Sum((M+C+A)_(in))” refers to the sum of a plurality of (M+C+A)_(in)values, each (M+C+A)_(in) value also may be a positive value and may beassociated with a corresponding measurement time interval as discussedbefore. In one embodiment, the same measurement interval may have both(M+C+A)_(out) as well as (M+C+A)_(in) values depending on the directionof the AC energy flow for M+C+A. The parameter “Sum(S)” refers to thesum of a plurality of S values determined over a corresponding pluralityof measurement intervals. The parameters “Eff_(IAC-DC)” and“Eff_(IDC-AC)” in equation (10) are the AC-DC conversion efficiency ofthe inverter and the DC-AC conversion efficiency of the inverter,respectively. These parameters are discussed later below. Furthermore,it is noted that the parameter referred to as “change in stored batteryenergy” in equation (10) should be multiplied with the battery'sdischarging efficiency if the parameter is negative and divided by thebattery's charging efficiency if the parameter is positive. However,these efficiencies are not mentioned in equation (10) above because thedelta (difference) in the stored energy is negligible enough over a longperiod of time and charging and discharging efficiencies may be closeenough to “1”.

From equation (10), the overall storage efficiency—that is, efficiencyof the system that can be attributed to battery storage, charge, anddischarge cycles—can be given as:Storage efficiency=[Sum((M+C+A)_(out))−(change in stored batteryenergy)*(Eff_(IDC-AC))]/[Sum(S)*(Eff_(IDC-AC))+Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))]  (11)

When energy storage system efficiency in equation (11) is evaluated overlong timeframes, such as, for example, over months or years, the changein the stored battery energy is insignificant in comparison to otherenergy flows in equation (11) and, hence, it can be ignored. In thatcase, equation (11) may be simplified to:Storageefficiency=Sum((M+C+A)_(out))/[Sum(S)*(Eff_(IDC-AC))+Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC)])  (12)

In particular embodiments, the monitoring unit 30 in the renewableenergy system 55 in FIG. 5 may be programmed to use the equation (12)above to determine efficiency of the energy storage, such as the storageunit 26 in FIG. 5, and the impact of the storage efficiency for thesystem as a whole.

In the equations (10)-(12) above, the parameter “Eff_(IDC-AC)” is theDC-to-AC conversion efficiency of the inverter (not shown) in theinverter unit 24, and the parameter “Eff_(IAC-DC)” is the AC-to-DCconversion efficiency of the inverter. Like the known or estimatedinverter efficiency (Eff_(I)) discussed before, the inverterefficiencies Eff_(IAC-DC) and Eff_(IDC-AC) also may be obtained orestimated as follows:

1. Nominal values for inverter-specific Eff_(IAC-DC) and Eff_(IDC-AC)may be obtained from the known inverter efficiency curves.

2. In one embodiment, when the battery current is zero (B=0), then theratio M_(out)/S may be used by the monitoring unit 30 to estimate theefficiency EFF_(IDC-AC). On the other hand, during a time interval whenS=0 and battery is charging, the monitoring unit 30 may use the ratioB/(M+C+A)_(in) to estimate the efficiency Eff_(IAC-DC).

The values of Eff_(IAC-DC) and Eff_(IDC-AC) obtained or estimated asnoted above can be substituted in equation (12) to determine the overallstorage efficiency and its impact for the system as a whole.

Case 3: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows forM+C+A are not Available.

When disaggregated (directional) flows ((M+C+A)_(out) and (M+C+A)_(in))are not available, short time interval based sampling may be used by themonitoring unit 30 to determine the M+C+A values, while assuming thatthe flow directions for M, C, and A are constant within the given timeinterval. Based on this assumption, measured values may be added by themonitoring unit 30 into separate “buckets” (like a storage memorylocation or register) based on direction so that the approach presentedin this case can be used. For example, assuming a short time interval of5 minutes, if the 5-minute net interval energy flow sum of M+C+A is fromthe grid to the inverter, it may be added to a register designated as an“(M+C+A)_(in) register,” and if the 5 minute interval energy flow isfrom the inverter to the grid, it may be added to a register designatedas an “(M+C+A)_(out) register.” The registers or memory locations may bepart of a memory—such as the memory 119 in FIG. 9—in the monitoring unit30. The monitoring unit 30 in the system 55 in FIG. 5 may then useequation (12) with the disaggregated values of M+C+A (that is,(M+C+A)_(in) and (M+C+A)_(out)) determined by the monitoring unit 30based on short time interval sampling to calculate the overallefficiency of the storage unit 26 in FIG. 5 and its operation, and theimpact of the storage efficiency for the system as a whole.

The table below summarizes the processing to be done by the monitoringunit 30 in the system 55 (FIG. 5) in each of the three cases discussedin Part II-B above:

Inverter can charge battery Inverter cannot charge from grid batteryfrom grid Disaggregated Case 2: Use equation (12) Case 1: Use equation(9) to flows to determine system storage determine storage availableefficiency efficiency Disaggregated Case 3: Disaggregate flows Case 1:Use equation (9) to flows not by short time interval determine storageavailable sampling, then use equation efficiency (12) to determinestorage efficiencyIII. AC-Coupled System with Critical and Auxiliary Loads

FIG. 7 is a simplified block diagram of an AC coupled renewable energysystem 83 (with critical and auxiliary loads) according to oneembodiment of the present disclosure showing various energy flows to bemeasured on a per-interval basis as per teachings of the presentdisclosure for calculations of renewable source production and systemstorage efficiency. It is noted here that although the systems in FIGS.5 and 7 are different from each other and different from the system 20in FIG. 3, for the sake of consistency and ease of discussion, the samereference numerals are used in FIGS. 3, 5, and 7 for systementities/units having the same or similar functionalities. Furthermore,also for the sake of consistency and ease of discussion, the samereference numeral “30” is used in FIGS. 3, 5, and 7 to refer to themonitoring unit generally. It is understood, however, that a monitoringunit designed to operate with one system may need to be modified (inhardware and/or software) to operate in the other because of differentenergy flows to be measured and different calculations to be performed,as discussed in more detail below.

In contrast to the system 55 in FIG. 5, the system 83 in FIG. 7 is anAC-coupled system where DC energy generated by the renewables source 22(illustrated by arrow 85 in FIG. 7) is converted into AC energy beforefeeding it to an inverter 87 connected to the battery unit 26. Suchconversion may be performed using a grid-tied inverter 89 coupled to therenewable DC energy source 22 (such as a PV solar array). Furthermore,in the AC-coupled system 83 of FIG. 7, a charge controller may be absentand the integrated inverter unit 24 of the DC-coupled systems 20, 55 maybe replaced by the battery inverter 87 (having inverter functionalityonly). In certain embodiments, energy flow metering may be integral tothe battery inverter 87 and/or the grid-tied inverter 89, which may beconfigured to be operatively connected with the monitoring unit 30 toperform metering and reporting of relevant energy flow measurements tothe monitoring unit 30 via their respective connections (shown by dottedarrows 91, 92)—direct or indirect (such as through a network). Like theconnections 34-35 and 61-62, one or more of the connections 91-92 may bewired or wireless, and may be via a communication network such as theInternet.

It is observed that, more generally, there may be five overall energyflows in the system 83 relevant to the discussion of FIG. 7: (i) theunidirectional AC energy flow from the renewable source 22 (for example,solar panels) to the critical loads panel 57 through the grid-tiedinverter 89 as represented by the exemplary arrow 95 in FIG. 7, (ii) thebi-directional AC energy flow to/from the battery inverter 87 from/tothe mains panel 28 as represented by the exemplary arrow 38 in FIG. 7,(iii) the bi-directional DC energy flow to/from the inverter 87 from/tothe battery unit 26 as represented by the exemplary arrow 39 in FIG. 7,(iv) the bi-directional AC energy flow between the inverter 87 and thecritical loads panel 57 as represented by the exemplary arrow 97 in FIG.7, and (v) the unidirectional AC energy flow from the battery inverter87 to the Aux loads panel 59 as represented by the exemplary arrow 65 inFIG. 7.

As mentioned before, in the embodiment of FIG. 7, the renewables output(at arrow 85) is converted to AC before it is connected to the batteryinverter 87. Therefore, for a pre-determined measurement time interval,the “S” value in the embodiment of FIG. 7 is the interval-specificmagnitude of AC energy flow from the grid-tied inverter 89 (placed onthe DC energy flow path 85 from the renewable source 22) to the criticalloads panel 57. Because the “S” value here represents AC energy (asopposed to DC energy in the embodiments of FIGS. 3 and 5), the dottedcircled letter “S” placed on the unidirectional arrow 95 is identifiedusing the reference numeral “99” to differentiate it from the earlier DC“S” values shown in FIGS. 3 and 5 using the reference numeral “42”. Theassociated AC energy flow is also identified using a different referencenumeral “95” to distinguish it from the DC energy flow 37 in FIGS. 3 and5.

In the system 83, the battery inverter 87 may serve the followingfunctions:

(i) It can act as a switch that connects the AC grid power from themains panel 28 through it to the critical loads panel 57, the aux loadspanel 59, and the renewables 22.

(ii) In case of a grid outage, it can disconnect the mains panel 28 fromcritical loads 57 and renewables 22 as well as aux loads 59.

(iii) In case of a grid outage, it can decide whether to connect therenewables 22 and critical loads 57 through to aux loads 59—that is,whether to use renewables to feed aux loads 59 if the renewables energyexceeds critical load demand.

(iv) It can convert DC energy from the batteries (not shown) in thebattery unit 26 and output AC energy to the critical loads panel 57and/or the aux loads panel 59 in case of a grid outage (at the mainspanel 28).

(iv) When the grid is fine, the inverter 87 can output AC energy to themains panel 28 and the aux loads panel 59, and also to the criticalloads panel 57 if the renewables 22 do not meet critical loads demand.

Like the M, C, and A values in the context of FIGS. 5-6, the M, C, and Avalues in the context of FIGS. 7-8 also may be defined as signednumbers. Thus, the following may apply in the context of FIGS. 7-8:

(i) The M value may be measured in the direction away from the batteryinverter 87. In other words, the M value may be positive when the ACenergy is flowing from the inverter 87 to the mains panel 28, andnegative when it is flowing from the mains panel 28 to the inverter 87.

(ii) The C value also may be measured in the direction away from theinverter 87. In other words, the C value may be positive when AC energyis flowing from the inverter 87 to the critical loads panel 57, andnegative when it is flowing from the critical loads panel 57 to theinverter 87. In the embodiment of FIG. 7, because the DC renewablesource 22 is connected up to the critical loads panel 57, this flow canbe positive or negative—as indicated by the bi-directional arrow 97.

(iii) The A value also may be measured in the direction away from theinverter 87. In other words, the A value may be positive when AC energyis flowing from the inverter 87 to the Aux loads panel 59, and negativewhen it is flowing from the Aux loads panel 59 to the inverter 87.Unless a second energy source is connected up to the aux loads panel 59that can feed power into the panel 59, this flow will always bepositive—as indicated by the unidirectional arrow 65.

It is noted here that, in some embodiments, the aux loads panel 59 andthe inverter unit's 87 connection to it may be optional and may simplynot exist. In that case, the A value may not exist and, hence, the Avalue be treated as zero in various equations given below.

Because the M, C, and A values are defined as signed numbers in thecontext of the embodiments in FIGS. 7-8, the net value of AC energy flowinto/out of the inverter 87 may be calculated before the magnitude ofthis net value is determined. Thus, any critical or aux loads being fedfrom the mains panel 28 can be cancelled out. In the discussion of FIGS.7-8, the expression “(M+C+A)” may refer to the magnitude of theinterval-specific net AC energy flow into/out of the battery inverter 87based on a directional summation of the M, C, and A values—a value willbe positive when its associated AC flow is out of the inverter 87 andnegative when its associated AC flow is into the inverter 87, as notedabove. In the embodiments of FIGS. 7-8, the net AC flow in the directionaway from the inverter 87 may be more relevant for renewables productionmeasurement in a storage-independent manner. Hence, in particularembodiments, the expression “(M+C+A)” may primarily refer to theinterval-specific net AC energy flow out of the inverter 87 as anabsolute value of a summation of the signed M, A, and C values.

For the system 83 in FIG. 7, the discussion below now addresses indetail two aspects of the present disclosure: (i) production measurementof renewable source in a storage-independent manner, and (ii)calculation of the system storage efficiency.

III-A. Renewable Source Production Measurement During a Set Interval.

In case of the AC coupled system 83 in FIG. 7, measuring renewablesproduction may be trivial in the sense that it can be obtained simply bymetering the AC output of the grid-tied inverter 89. Such metering maybe performed, for example, by installing an external AC sub-meter on theAC path 95 or through metering and information-sharing features builtinto the grid-tied inverter 89. As mentioned before, relevant energyflow information may be periodically conveyed to the monitoring unit 30(by the sub-meter or the inverter 89) or the monitoring unit 30 may take“snapshots” of the energy flow at arrow 95 at a pre-determined intervalsuch as, for example, every 5 minutes or every 15 minutes. The valuesassociated with each snapshot may be stored in the monitoring unit 30 todetermine the interval-specific renewables production in astorage-independent manner.

III-B. Deriving System Storage Efficiency.

As before, in determining system storage efficiency in the embodiment ofFIG. 7, two variables of the combination of renewable and storage systemmay be considered. The first variable is whether the battery inverter 87allows charging of the energy storage system 26 from the AC grid (viathe mains panel 28). The second variable is whether the available energyflow data in the renewable energy system 83 includes disaggregated(directional) flows in each direction for energy flow into and out ofthe battery and into and out of the inverter 87.

As mentioned before, relevant energy flow information may be conveyed tothe monitoring unit 30 either by installing dedicated AC or DCsub-metering equipment or through metering and information-sharingfeatures built into one or more of the units 22, 89, 87, 26, 28, 57, and59 in the system 83. In one embodiment, the monitoring unit 30 may take“snapshots” of the net energy flows at arrows 38-39, 65, 95, and 97 at apre-determined interval such as, for example, every 5 minutes or every15 minutes. The values associated with each snapshot may be stored inthe monitoring unit 30 for further processing as per teachings of thepresent disclosure. The snapshot interval may be set through softwareprogramming of the monitoring unit 30. In certain embodiments, theflow-reporting equipment (like a sub-meter) or unit 22, 89, 87, 26, 28,57, and 59 may be configured to measure and report the related flowinformation to the monitoring unit 30 at the set interval.Alternatively, the monitoring unit 30 itself may query eachequipment/unit periodically—at the set interval—for the measured flowvalue. In any event, for every flow-measurement period, the delta (ordifference) between the current and previous snapshots may be calculatedby the monitoring unit 30 to be used as interval-specific energy flows.

Case 1: Inverter Cannot Charge Energy Storage from Grid Power (that is,No AC to Dc Conversion).

Although this case has been analyzed in the context of the renewableenergy systems 20 (FIG. 3) and 55 (FIG. 5), this case is inapplicable tothe renewable energy system 83 in FIG. 7 because the system 83 isAC-coupled and, hence, the battery inverter 87 has to convert AC energyinto DC to charge the batteries 26. In the embodiment of FIG. 7, thereis no direct DC connection to the battery unit 26—such as, for example,through a charge controller as in case of the embodiments in FIGS. 3 and5.

Case 2: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows forM+C+A are Available.

In this case, the disaggregated flows of M (M_(out) and M_(in)) alonemay not be helpful because, depending on the consumption by critical andaux loads, M can be positive or negative even when the inverter 87 isoutputting AC energy. Therefore, it may be preferable to perform anaggregation of M+C+A when net M+C+A is positive separate from anaggregation of M+C+A when net M+C+A is negative. In particularembodiments, the battery inverter 87 may be configured to provide thisinformation natively because these are just separate sums of its ACoutputs and inflows, which may be recorded (for each measurement timeinterval) into two separate memory locations or registers (not shown) inthe inverter 87. The recorded sums of disaggregated energy flows of M,C, and A may be sent to the monitoring unit 30 to enable it to performthe calculations outlined below.

FIG. 8 depicts an exemplary flowchart illustrating how storageefficiency may be measured in the AC-coupled system 83 of FIG. 7according to one embodiment of the present disclosure. In particularembodiments, various tasks illustrated in FIG. 8 may be performed by themonitoring unit 30 (FIG. 7) to determine the storage efficiency of theDC storage unit 26. Thus, as noted at block 104 in FIG. 8, themonitoring unit 30 may determine each of the following three valuesduring a pre-determined time interval: (i) an “M” value, which is theinterval-specific magnitude of the first AC energy flow between aninverter (such as the battery inverter 87 in FIG. 7) and an ACinterconnect point (or Mains Panel) 28 in the system 83 as noted atblock 105; (ii) a “C” value, which is the interval-specific of a secondAC energy flow between the inverter 87 and a critical loads panel 57 inthe system 83 as noted at block 106; and (iii) an “A” value, which isthe interval-specific magnitude of a third AC energy flow from theinverter 87 to an auxiliary loads panel 59 in the system 83 as noted atblock 107. As noted at block 105, the DC storage unit 26 is operativelyconnected to the inverter 87 and configured to store DC energy.

Just for the sake of illustration, each of these M, C, and A values isshown in FIG. 7 as a dotted, circled letter 43 and 67-68 placed over therespective energy flow-indicating arrow 38, 97, and 65 to indicate theinterval-based measurement and analysis of the associated energy flow asper teachings of the present disclosure.

As noted at block 110 in FIG. 8 and discussed in more detail below, themonitoring unit 30 may determine a sum of (M+C+A)_(out) values. Each(M+C+A)_(out) value may be associated with a corresponding one of aplurality of pre-determined time intervals and may be aninterval-specific magnitude of net AC energy flow out of the inverter87.

Similarly, as noted at block 112 in FIG. 8, the monitoring unit 30 alsomay determine a sum of (M+C+A)_(in) values. Each (M+C+A)_(in) value maybe associated with a corresponding one of the plurality ofpre-determined time intervals and may be an interval-specific magnitudeof net AC energy flow into the inverter 87.

Furthermore, as also discussed in more detail below and as noted atblock 114 in FIG. 8, the monitoring unit 30 may calculate the efficiencyof the DC storage unit 26 using the sum of (M+C+A)_(out) values(determined at block 110), the sum of (M+C+A)_(in) values (determined atblock 112), a DC-to-AC conversion efficiency factor for the inverter 87,and an AC-to-DC conversion efficiency factor for the inverter 87.

Similar to the DC-coupled case in Part-II(B) above, by measuring M, C,and A values in the direction away from the battery inverter 87 (thatis, treating the M, C, and A values as positive when corresponding ACenergy flows are away from the inverter 87), and by having adisaggregated sum of M+C+A whenever M+C+A is net positive separate fromanother disaggregated sum of M+C+A whenever M+C+A is net negative, thefollowing relationship between M+C+A (which includes (M+C+A)_(out) aswell as (M+C+A)_(in)) and storage efficiency may be established over along term:Sum((M+C+A)_(out))=Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))*(storageefficiency)+(change in stored battery energy)*(Eff_(IDC-AC))  (13)

In the equation (13) above, the parameter “Sum((M+C+A)_(out))” refers tothe sum of a plurality of (M+C+A)_(out) values, each (M+C+A)_(out) valuemay be a positive value and may be associated with a correspondingmeasurement time interval as discussed before in more detail underPart-II. Similarly, the parameter “Sum((M+C+A)_(in))” refers to the sumof a plurality of (M+C+A)_(in) values, each (M+C+A)_(in) value also maybe a positive value and may be associated with a correspondingmeasurement time interval as discussed before. In one embodiment, thesame measurement interval may have both (M+C+A)_(out) as well as(M+C+A)_(in) values depending on the direction of the AC energy flow forM+C+A. The parameters “Eff_(IAC-DC)” and “Eff_(IDC-AC)” in equation (13)are the AC-DC conversion efficiency of the inverter 87 and the DC-ACconversion efficiency of the inverter 87, respectively. These parametersare discussed later below. Furthermore, it is noted that the parameterreferred to as “change in stored battery energy” in equation (13) shouldbe multiplied with the battery's discharging efficiency if the parameteris negative and divided by the battery's charging efficiency if theparameter is positive. However, these efficiencies are not mentioned inequation (13) above because the delta (difference) in the stored energyis negligible enough over a long period of time and charging anddischarging efficiencies may be close enough to “1”.

From equation (13), the overall storage efficiency—that is, efficiencyof the system that can be attributed to battery storage, charge, anddischarge cycles—can be given as:Storage efficiency=[Sum((M+C+A)_(out))−(change in stored batteryenergy)*(Eff_(IDC-AC))]/[Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))]  (14)

When energy storage system efficiency in equation (14) is evaluated overlong timeframes, such as, for example, over months or years, the changein the stored battery energy is insignificant in comparison to otherenergy flows in equation (14) and, hence, it can be ignored. In thatcase, equation (14) may be simplified to:Storageefficiency=Sum((M+C+A)_(out))/[Sum((M+C+A)_(in))*(Eff_(IAC-DC))*(Eff_(IDC-AC))]  (15)

In particular embodiments, the monitoring unit 30 in the renewableenergy system 83 in FIG. 7 may be programmed to use the equation (15)above to determine efficiency of the energy storage, such as the storageunit 26 in FIG. 7, and the impact of the storage efficiency for thesystem as a whole. Furthermore, as mentioned earlier, in someembodiments, the battery inverter 87 can itself directly aggregate netpositive M+C+A total flows and net negative M+C+A total flows as twoseparate summations of the net AC energy output by the battery inverter87 and the net AC energy consumed by the battery inverter 87. Thesesummations may be recorded (for each measurement time interval) into twoseparate memory locations or registers (not shown) in the inverter 87and may be sent to the monitoring unit 30 to enable it to perform thecalculations outlined above.

In the equations (13)-(15) above, the parameter “Eff_(IDC-AC)” is theDC-to-AC conversion efficiency of the inverter 87 only, and theparameter “Eff_(IAC-DC)” is the AC-to-DC conversion efficiency of theinverter 87 only. In other words, these efficiencies pertain to thebattery inverter 87 alone, and not to the grid-tied inverter 89. Asbefore, the inverter efficiencies Eff_(IAC-DC) and Eff_(IDC-AC) may beobtained or estimated as follows:

1. Nominal values for inverter-specific Eff_(IAC-DC) and Eff_(IDC-AC)may be obtained from the known inverter efficiency curves for thebattery inverter 87.

2. In one embodiment, when the battery 26 is discharging, the ratio(M+C+A)_(out)/B may be used by the monitoring unit 30 to estimate theefficiency Eff_(IDC-AC). On the other hand, during a time interval whenthe battery 26 is charging, the monitoring unit 30 may use the ratioB/(M+C+A)_(in) to estimate the efficiency Eff_(IAC-DC).

The values of Eff_(IAC-DC) and Eff_(IDC-AC) obtained or estimated asnoted above can be substituted in equation (15) to determine the overallstorage efficiency and its impact for the system as a whole.

Case 3: Inverter can Charge Energy Storage from Grid Power (that is, ACto DC Conversion is Present) and Disaggregated (Directional) Flows forM+C+A are not Available.

This case addresses a scenario when separate negative and positivetotals for M+C+A are not available from the inverter 87. Whendisaggregated (directional) flows ((M+C+A)_(out) and (M+C+A)_(in)) arenot available, short time interval based sampling may be used by themonitoring unit 30 to determine the M+C+A values, while assuming thatthe flow directions for M, C, and A are constant within the given timeinterval. Based on this assumption, measured values may be added by themonitoring unit 30 into separate “buckets” (like a storage memorylocation or register) based on direction so that the approach presentedin this case can be used. The monitoring unit 30 may accumulate M+C+Apositives in one register and M+C+A negatives in another register. Forexample, assuming a short time interval of 5 minutes, if the 5-minutenet interval energy flow sum of M+C+A is into the inverter 87, it may beadded to a register designated as an “(M+C+A)_(in) register,” and if the5 minute interval energy flow is away from the inverter, it may be addedto a register designated as an “(M+C+A)_(out) register.” The registersor memory locations may be part of a memory—such as the memory 119 inFIG. 9—in the monitoring unit 30. The monitoring unit 30 in the system83 in FIG. 7 may then use equation (15) with the disaggregated values ofM+C+A (that is, (M+C+A)_(in) and (M+C+A)_(out)) determined by themonitoring unit 30 based on short time interval sampling to calculatethe overall efficiency of the storage unit 26 in FIG. 7 and itsoperation, and the impact of the storage efficiency for the system as awhole.

The table below summarizes the processing to be done by the monitoringunit 30 in the system 83 (FIG. 7) in each of the three cases discussedin Part III-B above:

Inverter can charge battery Inverter cannot charge from grid batteryfrom grid Disaggregated Case 2: Use equation (15) to Case 1: notapplicable flows available determine system storage efficiencyDisaggregated Case 3: Disaggregate flows Case 1: not applicable flowsnot by short time interval available sampling, then use equation (15) todetermine storage efficiency

FIG. 9 depicts an exemplary block diagram of a monitoring unit accordingto one embodiment of the present disclosure. The monitoring unit in FIG.9 may be the monitoring unit 30 from any of the embodiments in FIGS. 3,5, and 7. The monitoring unit 30 may be suitably configured—in hardwareand/or software—to implement the storage-independent measurement ofrenewable source production and determination of system storageefficiency according to the teachings of the present disclosure. Themonitoring unit 30 may include a processor 116 and ancillary hardware toaccomplish various processing aspects discussed before. The processor116 may be configured to interface with a number of external devices. Inone embodiment, a number of input devices 118 may be part of themonitoring unit 30 and may provide data inputs—such as user input, andthe like—to the processor 116 for further processing. The input devices118 may include, for example, a touchpad, a camera, an image sensor, aproximity sensor, a Global Positioning System (GPS) sensor, a computerkeyboard, a touch-screen, a joystick, a physical or virtual “clickablebutton,” a computer mouse/pointing device, and the like. In FIG. 9, theprocessor 116 is shown coupled to a system memory 119, a peripheralstorage unit 121, one or more output devices 122, and a networkinterface (or interface unit) 123. A display screen is an example of anoutput device 122. In some embodiments, the unit 30 may include morethan one instance of the devices shown.

In various embodiments, all of the components shown in FIG. 9 may behoused within a single housing. Thus, the monitoring unit 30 may beconfigured as a standalone computer or data processing system—such as,for example, a laptop or a desktop computer, a mobile device, a tabletcomputer, or a single-board computer—or in any other suitable formfactor. In some embodiments, the monitoring unit 30 may be configured asa client system rather than a server system. In other embodiments, themonitoring unit 30 may be a mobile wireless device such as, for example,a cellular phone, a smartphone or tablet, or a User Equipment (UE),suitably configured to perform various tasks as per teachings of thepresent disclosure.

In particular embodiments, the monitoring unit 30 may include more thanone processor (e.g., in a distributed processing configuration). Whenthe monitoring unit 30 is a multiprocessor system, there may be morethan one instance of the processor 116 or there may be multipleprocessors coupled to the processor 116 via their respective interfaces(not shown). The processor 116 may be a System on Chip (SoC) and/or mayinclude more than one Central Processing Units (CPUs).

The system memory 119 may be any semiconductor-based storage system suchas, for example, Dynamic Random Access Memory (DRAM), Static RAM (SRAM),Synchronous DRAM (SDRAM), Rambus® DRAM, flash memory, register-basedstorage, various types of Read Only Memory (ROM), and the like. In someembodiments, the memory 119 may include multiple different types ofsemiconductor memories, as opposed to a single type of memory. In otherembodiments, the memory 119 may be a non-transitory data storage medium.

The peripheral storage unit 121, in various embodiments, may includesupport for magnetic, optical, magneto-optical, or solid-state storagemedia such as hard drives, optical disks (such as Compact Disks (CDs) orDigital Versatile Disks (DVDs)), Non-volatile Random Access Memory(NVRAM) devices, Secure Digital (SD) memory cards (including MicroSDmemories), Universal Serial Bus (USB) memories, and the like. In someembodiments, the peripheral storage unit 121 may be coupled to theprocessor 116 via a standard peripheral interface such as a SmallComputer System Interface (SCSI) interface, a Fibre Channel interface, aFirewire® (IEEE 1394) interface, a Peripheral Component InterfaceExpress (PCI Express™) standard based interface, a USB protocol basedinterface, a Bluetooth® interface, or another suitable interface.Various such storage devices may be non-transitory data storage media.

As mentioned earlier, a display screen may be an example of the outputdevice 122. Other examples of an output device include agraphics/display device, a Liquid Crystal Display (LCD) screen, acomputer screen, an alarm system, a CAD/CAM (Computer AidedDesign/Computer Aided Machining) system, a smartphone display screen, orany other type of data output device. In some embodiments, the inputdevice(s) 118 and the output device(s) 122 may be coupled to theprocessor 116 via an I/O (Input/Output) or peripheral interface(s).

In one embodiment, the network interface 123 may communicate with theprocessor 116 to enable the unit 30 to couple to a communication networksuch as, for example, the Internet. In another embodiment, the interfaceunit 123 may provide the electrical connectivity—wired or wireless—tocommunicate with various units, such as the units 22, 24, 26, 28, 57,59, 87, 89 (depending on the system 20, 55, or 83), and dedicatedsub-metering equipment(s), if any, in the respective system 20, 55, or83. In one embodiment, the network interface 123 may be absentaltogether. The interface unit 123 may include any suitable devices,media and/or protocol content for connecting the monitoring unit 30 to anetwork—whether wired or wireless—and also to various equipment in thesystem 20, 55, or 83. In various embodiments, as mentioned before, thenetwork may include a Local Area Network (LAN), a Wide Area Network(WAN), a wired or wireless Ethernet, a telecommunication network, orother suitable type of network.

The monitoring unit 30 may include an on-board power supply unit 125(which may be optional in some embodiments) to provide electrical powerto various system components illustrated in FIG. 9. The power supplyunit 125 may receive batteries or may be connectable to an AC electricalpower outlet. In one embodiment, the power supply unit 125 may convertsolar energy or other renewable energy into electrical power.

In one embodiment, a non-transitory, computer-readable data storagemedium, such as, for example, the system memory 119 or a peripheral datastorage unit, such as a MicroSD memory card, may store program code orsoftware. The processor 116 may be configured to execute the programcode, whereby the monitoring unit 30 may be operative to perform therenewable source production measurement and storage efficiencydetermination as discussed hereinbefore—such as, for example, theoperations discussed earlier with reference to FIGS. 3-8. The programcode or software may be proprietary software or open source softwarewhich, upon execution by the processor 116 may enable the monitoringunit 30 to receive time interval based energy flow data from differententities in the renewable energy system 20, 55, or 83, use the receiveddata to determine the production measurement for a renewable source in astorage-independent manner, derive system storage efficiency from thedata received over a long period of time using various equations givenbefore, and so on.

In the preceding description, for purposes of explanation and notlimitation, specific details are set forth (such as particulararchitectures, interfaces, techniques, etc.) in order to provide athorough understanding of the disclosed technology. However, it will beapparent to those skilled in the art that the disclosed technology maybe practiced in other embodiments that depart from these specificdetails. That is, those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the disclosed technology. In someinstances, detailed descriptions of well-known devices, circuits, andmethods are omitted so as not to obscure the description of thedisclosed technology with unnecessary detail. All statements hereinreciting principles, aspects, and embodiments of the disclosedtechnology, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, such as, for example, any elements developed that perform thesame function, regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat block diagrams herein (e.g., in FIGS. 3, 5, 7, and 9) can representconceptual views of illustrative circuitry or other functional unitsembodying the principles of the technology. Similarly, it will beappreciated that the flowcharts in FIGS. 4, 6, and 8 represent variousprocesses which may be substantially performed by a processor (e.g., theprocessor 116 in FIG. 9). Such a processor may include, by way ofexample, a general purpose processor, a special purpose processor, aconventional processor, a digital signal processor (DSP), a plurality ofmicroprocessors, one or more microprocessors in association with a DSPcore, a controller, a microcontroller, Application Specific IntegratedCircuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, anyother type of integrated circuit (IC), and/or a state machine. Some orall of the functionalities described above in the context of FIGS. 3-8also may be provided by such a processor, in the hardware and/orsoftware. The processor 116 may employ distributed processing in certainembodiments.

When certain inventive aspects require software-based processing, suchsoftware or program code may reside in a computer-readable data storagemedium. As noted earlier, such data storage medium may be part of theperipheral storage 121, or may be part of the system memory 119, or theprocessor's 116 internal memory (not shown). In one embodiment, theprocessor 116 may execute instructions stored on such a medium to carryout the software-based processing. The computer-readable data storagemedium may be a non-transitory data storage medium containing a computerprogram, software, firmware, or microcode for execution by a generalpurpose computer or a processor mentioned above. Examples of suchcomputer-readable storage media include a ROM, a RAM, a digitalregister, a cache memory, semiconductor memory devices, magnetic mediasuch as internal hard disks, magnetic tapes and removable disks,magneto-optical media, and optical media such as CD-ROM disks and DVDs.

Alternative embodiments of the monitoring unit 30 according to inventiveaspects of the present disclosure may include additional componentsresponsible for providing additional functionality, including any of thefunctionality identified above and/or any functionality necessary tosupport the solution as per the teachings of the present disclosure.Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features. As mentioned before, various monitoring unit-basedprocessing functions discussed herein may be provided through the use ofhardware (such as circuit hardware) and/or hardware capable of executingsoftware/firmware in the form of coded instructions or microcode storedon a non-transitory, computer-readable data storage medium (mentionedabove). Thus, such functions and illustrated functional/flowchart blocksare to be understood as being either hardware-implemented and/orcomputer-implemented, and thus machine-implemented.

The foregoing describes a system and method in which productionmeasurement for renewable energy is obtained in a storage-independentmanner—in a form that would be comparable to renewable installationswithout storage. Thus, energy storage is separated out from therenewable generation to provide individual performance analytics forboth in DC-coupled and AC-coupled renewable energy systems with criticaland auxiliary loads. A monitoring unit uses device communication andmetering to enable revenue-grade production measurement for a renewablesource and energy storage periodically at specified time intervals. Theproduction measurement for a renewable source is obtained in a form thatwould be comparable to renewable installations without storage, which isimportant for accurate billing, maintenance, and performance analytics.Additionally, multiple energy flows may be used by the monitoring unitto arrive at a storage efficiency value that can be attributed to thestorage unit as well as how the storage unit is operated in therenewable energy system. Thus, the storage efficiency quantifiesefficiency losses arising from the use of a storage unit to estimate theactual impact of storage and, possibly, the charge controller algorithmon energy production.

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a wide range of applications. Accordingly, the scope of patentedsubject matter should not be limited to any of the specific exemplaryteachings discussed above, but is instead defined by the followingclaims.

What is claimed is:
 1. A method for measuring production of renewableenergy in a storage-independent manner in a renewable energy system,said method comprising: determining each of the following values duringa pre-determined time interval: an “S” value, wherein the S value is aninterval-specific magnitude of a first Direct Current (DC) energy flowfrom a renewable energy source to an intermediate unit in the system, an“M” value, wherein the M value is an interval-specific magnitude of afirst Alternating Current (AC) energy flow between the intermediate unitand an AC interconnect point in the system, a “C” value, wherein the Cvalue is an interval-specific magnitude of a second AC energy flow fromthe intermediate unit to a critical loads panel in the system, an “A”value, wherein the A value is an interval-specific magnitude of a thirdAC energy flow from the intermediate unit to an auxiliary loads panel inthe system, and a “B” value, wherein the B value is an interval-specificmagnitude of a second DC energy flow between the intermediate unit and aDC storage unit in the system; further determining an interval-specificnet AC energy flow out of the intermediate unit based on a directionalsummation of the M, C, and A values; and using the S, M, C, A, and Bvalues to calculate a portion of the interval-specific net AC energyflow attributable only to the interval-specific first DC energy flow,thereby excluding contribution to the net AC energy flow from the DCstorage unit.
 2. The method of claim 1, wherein the A value is zero. 3.The method of claim 1, wherein determining the interval-specific net ACenergy flow includes: generating signed M, A, and C values by performingthe following: treating the A and C values as positive values, furthertreating the M value as one of the following: a positive M value when adirection of the interval-specific first AC energy flow is out of theintermediate unit, and a negative M value when the direction of theinterval-specific first AC energy flow is into the intermediate unit;and determining the interval-specific net AC energy flow out of theintermediate unit as an absolute value of a summation of the signed M,A, and C values.
 4. The method of claim 1, wherein the renewable energyis solar energy, and wherein the renewable energy system is aPhotovoltaic (PV) solar system.
 5. The method of claim 1, wherein theportion is one of the following: a first ratio calculated as(M+C+A)*S/(S+B) when the renewable energy source is net generating, theDC storage unit is net discharging, and the net AC energy flow out ofthe intermediate unit is positive; a second ratio calculated as(M+C+A)*S/(S−B) when the renewable energy source is net generating, theDC storage unit is net charging, and the net AC energy flow out of theintermediate unit is positive; and a third ratio given by−1*(M+C+A)*S*E/(B−S) when the renewable energy source is net generating,the DC storage unit is net charging, and the net AC energy flow out ofan inverter in the intermediate unit is negative, wherein “E” is around-trip efficiency factor for the inverter.
 6. The method of claim 1,wherein the intermediate unit includes an inverter and a chargecontroller.
 7. The method of claim 6, further comprising: determiningthe following: a sum of S values, wherein each S value in the sum isassociated with a corresponding one of a plurality of pre-determinedtime intervals, and a sum of (M+C+A) values, wherein each (M+C+A) valuein the sum is associated with a corresponding one of the plurality ofpre-determined time intervals; and calculating an efficiency of the DCstorage unit using the sum of S values, the sum of (M+C+A) values, andan efficiency factor for the inverter.
 8. The method of claim 7, whereinusing the S, M, C, A, and B values includes: estimating the efficiencyfactor for the inverter as a ratio of the M value divided by the S valuewhen the B value is zero.
 9. The method of claim 6, further comprising:determining the following: a sum of S values, wherein each S value inthe sum is associated with a corresponding one of a plurality ofpre-determined time intervals, a sum of (M+C+A)_(out) values, whereineach (M+C+A)_(out) value is associated with a corresponding one of theplurality of pre-determined time intervals and is an interval-specificmagnitude of net AC energy flow out of the inverter, and a sum of(M+C+A)_(in) values, wherein each (M+C+A)_(in) value is a negative valueand is associated with a corresponding one of the plurality ofpre-determined time intervals, and wherein each (M+C+A)_(in) value is aninterval-specific magnitude of net AC energy flow into the inverter; andcalculating an efficiency of the DC storage unit using the sum of Svalues, the sum of (M+C+A)_(out) values, the sum of (M+C+A)_(in) values,a DC-to-AC conversion efficiency factor for the inverter, and anAC-to-DC conversion efficiency factor for the inverter.
 10. The methodof claim 9, wherein using the S, M, C, A, and B values includesperforming at least one of the following: estimating the DC-to-ACconversion efficiency factor for the inverter as a ratio of an M_(out)value divided by a corresponding S value when the B value is zero; andestimating the AC-to-DC conversion efficiency factor for the inverter asa ratio of a B value and a corresponding (M+C+A)_(in) value when the Svalue is zero and the DC storage unit is net charging.
 11. The method ofclaim 1, further comprising: generating pricing for theinterval-specific first DC energy flow based on the calculated portionof the interval-specific net AC energy flow.
 12. A method for measuringan efficiency of a Direct Current (DC) storage unit in a renewableenergy system, said method comprising: determining a sum of “S” values,wherein each S value in the sum is associated with a corresponding oneof a plurality of pre-determined time intervals and is aninterval-specific magnitude of a DC energy flow from a renewable energysource to an inverter in the system, and wherein the DC storage unit isoperatively connected to the inverter and configured to store DC energy;further determining a sum of (M+C+A) values, wherein each (M+C+A) valuein the sum of (M+C+A) values is associated with a corresponding one ofthe plurality of pre-determined time intervals and includes: an “M”value that is an interval-specific magnitude of a first AlternatingCurrent (AC) energy flow between the inverter and an AC interconnectpoint in the system, a “C” value that is an interval-specific magnitudeof a second AC energy flow from the inverter to a critical loads panelin the system, and an “A” value that is an interval-specific magnitudeof a third AC energy flow from the inverter to an auxiliary loads panelin the system; and calculating the efficiency of the DC storage unitusing the sum of S values, the sum of (M+C+A) values, and an efficiencyfactor for the inverter.
 13. The method of claim 12, further comprising:determining the sum of (M+C+A) values by: determining a sum of(M+C+A)_(out) values, wherein each (M+C+A)_(out) value is associatedwith a corresponding one of the plurality of pre-determined timeintervals and is an interval-specific magnitude of net AC energy flowout of the inverter, and determining a sum of (M+C+A)_(in) values,wherein each (M+C+A)_(in) value is associated with a corresponding oneof the plurality of pre-determined time intervals and is aninterval-specific magnitude of net AC energy flow into the inverter; andcalculating the efficiency of the DC storage unit using the sum of Svalues, the sum of (M+C+A)_(out) values, the sum of (M+C+A)_(in) values,a DC-to-AC conversion efficiency factor for the inverter, and anAC-to-DC conversion efficiency factor for the inverter, wherein theefficiency factor for the inverter includes the DC-to-AC conversionefficiency factor and the AC-to-DC conversion efficiency factor.
 14. Amethod for determining an efficiency of a Direct Current (DC) storageunit in a renewable energy system, said method comprising: determiningeach of the following values during a pre-determined time interval: an“M” value that is an interval-specific magnitude of a first AlternatingCurrent (AC) energy flow between an inverter and an AC interconnectpoint in the system, wherein the DC storage unit is operativelyconnected to the inverter and configured to store DC energy, a “C” valuethat is an interval-specific magnitude of a second AC energy flowbetween the inverter and a critical loads panel in the system, and an“A” value that is an interval-specific magnitude of a third AC energyflow from the inverter to an auxiliary loads panel in the system;determining a sum of (M+C+A)_(out) values, wherein each (M+C+A)_(out)value is associated with a corresponding one of a plurality ofpre-determined time intervals and is an interval-specific magnitude ofnet AC energy flow out of the inverter; determining a sum of(M+C+A)_(in) values, wherein each (M+C+A)_(in) value is associated witha corresponding one of the plurality of pre-determined time intervalsand is an interval-specific magnitude of net AC energy flow into theinverter; and calculating the efficiency of the DC storage unit usingthe sum of (M+C+A)_(out) values, the sum of (M+C+A)_(in) values, aDC-to-AC conversion efficiency factor for the inverter, and an AC-to-DCconversion efficiency factor for the inverter.
 15. A monitoring unit formeasuring production of renewable energy in a storage-independent mannerin a renewable energy system, said monitoring unit operable to performthe following: determine each of the following values during apre-determined time interval: an “S” value, wherein the S value is aninterval-specific magnitude of a first Direct Current (DC) energy flowfrom a renewable energy source to an intermediate unit in the system, an“M” value, wherein the M value is an interval-specific magnitude of afirst Alternating Current (AC) energy flow between the intermediate unitand an AC interconnect point in the system, a “C” value, wherein the Cvalue is an interval-specific magnitude of a second AC energy flow fromthe intermediate unit to a critical loads panel in the system, an “A”value, wherein the A value is an interval-specific magnitude of a thirdAC energy flow from the intermediate unit to an auxiliary loads panel inthe system, and a “B” value, wherein the B value is an interval-specificmagnitude of a second DC energy flow between the intermediate unit and aDC storage unit in the system; further determine an interval-specificnet AC energy flow out of the intermediate unit based on a directionalsummation of the M, C, and A values; and use the S, M, C, A, and Bvalues to calculate a portion of the interval-specific net AC energyflow attributable only to the interval-specific first DC energy flow,thereby excluding contribution to the net AC energy flow from the DCstorage unit.
 16. The monitoring unit of claim 15, wherein themonitoring unit is operable to further perform at least one of thefollowing: calculate the portion as a first ratio given by(M+C+A)*S/(S+B) when the renewable energy source is net generating, theDC storage unit is net discharging, and the net AC energy flow out ofthe intermediate unit is positive; calculate the portion as a secondratio given by (M+C+A)*S/(S−B) when the renewable energy source is netgenerating, the DC storage unit is net charging, and the net AC energyflow out of the intermediate unit is positive; and calculate the portionas a third ratio given by −1*(M+C+A)*S*E/(B−S) when the renewable energysource is net generating, the DC storage unit is net charging, and thenet AC energy flow out of an inverter in the intermediate unit isnegative, wherein “E” is a round-trip efficiency factor for theinverter.
 17. The monitoring unit of claim 15, wherein the monitoringunit is operable to further perform the following: determine a sum of Svalues, wherein each S value in the sum is associated with acorresponding one of a plurality of pre-determined time intervals;determine a sum of (M+C+A)_(out) values, wherein each (M+C+A)_(out)value is associated with a corresponding one of the plurality ofpre-determined time intervals and is an interval-specific magnitude ofnet AC energy flow out of an inverter in the intermediate unit; anddetermine a sum of (M+C+A)_(in) values, wherein each (M+C+A)_(in) valueis a negative value and is associated with a corresponding one of theplurality of pre-determined time intervals, and wherein each(M+C+A)_(in) value is an interval-specific magnitude of net AC energyflow into the inverter; and calculate an efficiency of the DC storageunit using the sum of S values, the sum of (M+C+A)_(out) values, the sumof (M+C+A)_(in) values, a DC-to-AC conversion efficiency factor for theinverter, and an AC-to-DC conversion efficiency factor for the inverter.18. A data storage medium operable with a monitoring unit in a renewableenergy system and containing program instructions, which, when executedby the monitoring unit, cause the monitoring unit to perform thefollowing: determine each of the following values during apre-determined time interval: an “S” value, wherein the S value is aninterval-specific magnitude of a first Direct Current (DC) energy flowfrom a renewable energy source to an intermediate unit in the system, an“M” value, wherein the M value is an interval-specific magnitude of afirst Alternating Current (AC) energy flow between the intermediate unitand an AC interconnect point in the system, a “C” value, wherein the Cvalue is an interval-specific magnitude of a second AC energy flow fromthe intermediate unit to a critical loads panel in the system, an “A”value, wherein the A value is an interval-specific magnitude of a thirdAC energy flow from the intermediate unit to an auxiliary loads panel inthe system, and a “B” value, wherein the B value is an interval-specificmagnitude of a second DC energy flow between the intermediate unit and aDC storage unit in the system; further determine an interval-specificnet AC energy flow out of the intermediate unit based on a directionalsummation of the M, C, and A values; and use the S, M, C, A, and Bvalues to calculate a portion of the interval-specific net AC energyflow attributable only to the interval-specific first DC energy flow,thereby measuring production of renewable energy by the renewable energysource in a storage-independent manner.
 19. The data storage medium ofclaim 18, wherein the program instructions, when executed by themonitoring unit, cause the monitoring unit to further perform thefollowing: determine a sum of S values, wherein each S value in the sumis associated with a corresponding one of a plurality of pre-determinedtime intervals; determine a sum of (M+C+A)_(out) values, wherein each(M+C+A)_(out) value is associated with a corresponding one of theplurality of pre-determined time intervals and is an interval-specificmagnitude of net AC energy flow out of an inverter in the intermediateunit; and determine a sum of (M+C+A)_(in) values, wherein each(M+C+A)_(in) value is associated with a corresponding one of theplurality of pre-determined time intervals, and wherein each(M+C+A)_(in) value is an interval-specific magnitude of net AC energyflow into the inverter; and calculate an efficiency of the DC storageunit using the sum of S values, the sum of (M+C+A)_(out) values, the sumof (M+C+A)_(in) values, a DC-to-AC conversion efficiency factor for theinverter, and an AC-to-DC conversion efficiency factor for the inverter.20. The data storage medium of claim 18, wherein the renewable energy issolar energy, and wherein the renewable energy system is a Photovoltaic(PV) solar system.